The sqrt function is a value returning function, specifically the square root of the argument of the function. The main function in a C program is typically a. Lecturer You're probably wondering,so what are the parts required for a C program?We will learn how to structure a C programby exploring a program called Hello, World.I'm already inside my Dev-C IDE.I'm going to create a new project.I'm going to go to file, new, and I'm going to click on project.Notice under the new project, under the tab basic,I can choose to.

Functions allow to structure programs in segments of code to perform individual tasks.
In C++, a function is a group of statements that is given a name, and which can be called from some point of the program. The most common syntax to define a function is:
type name ( parameter1, parameter2, ...) { statements }

Where:
- type is the type of the value returned by the function.
- name is the identifier by which the function can be called.
- parameters (as many as needed): Each parameter consists of a type followed by an identifier, with each parameter being separated from the next by a comma. Each parameter looks very much like a regular variable declaration (for example: int x), and in fact acts within the function as a regular variable which is local to the function. The purpose of parameters is to allow passing arguments to the function from the location where it is called from.
- statements is the function's body. It is a block of statements surrounded by braces { } that specify what the function actually does.
Let's have a look at an example:
This program is divided in two functions: addition and main. Remember that no matter the order in which they are defined, a C++ program always starts by calling main. In fact, main is the only function called automatically, and the code in any other function is only executed if its function is called from main (directly or indirectly).
In the example above, main begins by declaring the variable z of type int, and right after that, it performs the first function call: it calls addition. The call to a function follows a structure very similar to its declaration. In the example above, the call to addition can be compared to its definition just a few lines earlier:
The parameters in the function declaration have a clear correspondence to the arguments passed in the function call. The call passes two values, 5 and 3, to the function; these correspond to the parameters a and b, declared for function addition.
At the point at which the function is called from within main, the control is passed to function addition: here, execution of main is stopped, and will only resume once the addition function ends. At the moment of the function call, the value of both arguments (5 and 3) are copied to the local variables int a and int b within the function.
Then, inside addition, another local variable is declared (int r), and by means of the expression r=a+b, the result of a plus b is assigned to r; which, for this case, where a is 5 and b is 3, means that 8 is assigned to r.
The final statement within the function:

Ends function addition, and returns the control back to the point where the function was called; in this case: to function main. At this precise moment, the program resumes its course on main returning exactly at the same point at which it was interrupted by the call to addition. But additionally, because addition has a return type, the call is evaluated as having a value, and this value is the value specified in the return statement that ended addition: in this particular case, the value of the local variable r, which at the moment of the return statement had a value of 8.
Therefore, the call to addition is an expression with the value returned by the function, and in this case, that value, 8, is assigned to z. It is as if the entire function call (addition(5,3)) was replaced by the value it returns (i.e., 8).
Then main simply prints this value by calling:
A function can actually be called multiple times within a program, and its argument is naturally not limited just to literals:

Similar to the addition function in the previous example, this example defines a subtract function, that simply returns the difference between its two parameters. This time, main calls this function several times, demonstrating more possible ways in which a function can be called.
Let's examine each of these calls, bearing in mind that each function call is itself an expression that is evaluated as the value it returns. Again, you can think of it as if the function call was itself replaced by the returned value:
If we replace the function call by the value it returns (i.e., 5), we would have:

With the same procedure, we could interpret:
as:

since 5 is the value returned by subtraction (7,2).
In the case of:
The arguments passed to subtraction are variables instead of literals. That is also valid, and works fine. The function is called with the values x and y have at the moment of the call: 5 and 3 respectively, returning 2 as result.
The fourth call is again similar:

The only addition being that now the function call is also an operand of an addition operation. Again, the result is the same as if the function call was replaced by its result: 6. Note, that thanks to the commutative property of additions, the above can also be written as:
With exactly the same result. Note also that the semicolon does not necessarily go after the function call, but, as always, at the end of the whole statement. Again, the logic behind may be easily seen again by replacing the function calls by their returned value:

Functions with no type. The use of void

The syntax shown above for functions:
type name ( argument1, argument2 ...) { statements }

Requires the declaration to begin with a type. This is the type of the value returned by the function. But what if the function does not need to return a value? In this case, the type to be used is void, which is a special type to represent the absence of value. For example, a function that simply prints a message may not need to return any value:
void can also be used in the function's parameter list to explicitly specify that the function takes no actual parameters when called. For example, printmessage could have been declared as:

In C++, an empty parameter list can be used instead of void with same meaning, but the use of void in the argument list was popularized by the C language, where this is a requirement.
Something that in no case is optional are the parentheses that follow the function name, neither in its declaration nor when calling it. And even when the function takes no parameters, at least an empty pair of parentheses shall always be appended to the function name. See how printmessage was called in an earlier example:
The parentheses are what differentiate functions from other kinds of declarations or statements. The following would not call the function:

The return value of main

You may have noticed that the return type of main is int, but most examples in this and earlier chapters did not actually return any value from main.
Well, there is a catch: If the execution of main ends normally without encountering a return statement the compiler assumes the function ends with an implicit return statement:
Note that this only applies to function main for historical reasons. All other functions with a return type shall end with a proper return statement that includes a return value, even if this is never used.
When main returns zero (either implicitly or explicitly), it is interpreted by the environment as that the program ended successfully. Other values may be returned by main, and some environments give access to that value to the caller in some way, although this behavior is not required nor necessarily portable between platforms. The values for main that are guaranteed to be interpreted in the same way on all platforms are:

value	description
0	The program was successful
EXIT_SUCCESS	The program was successful (same as above). This value is defined in header '><cstdlib>.
EXIT_FAILURE	The program failed. This value is defined in header '><cstdlib>.

Because the implicit return 0; statement for main is a tricky exception, some authors consider it good practice to explicitly write the statement.

Arguments passed by value and by reference

In the functions seen earlier, arguments have always been passed by value. This means that, when calling a function, what is passed to the function are the values of these arguments on the moment of the call, which are copied into the variables represented by the function parameters. For example, take:

In this case, function addition is passed 5 and 3, which are copies of the values of x and y, respectively. These values (5 and 3) are used to initialize the variables set as parameters in the function's definition, but any modification of these variables within the function has no effect on the values of the variables x and y outside it, because x and y were themselves not passed to the function on the call, but only copies of their values at that moment.
In certain cases, though, it may be useful to access an external variable from within a function. To do that, arguments can be passed by reference, instead of by value. For example, the function duplicate in this code duplicates the value of its three arguments, causing the variables used as arguments to actually be modified by the call:
To gain access to its arguments, the function declares its parameters as references. In C++, references are indicated with an ampersand (&) following the parameter type, as in the parameters taken by duplicate in the example above.
When a variable is passed by reference, what is passed is no longer a copy, but the variable itself, the variable identified by the function parameter, becomes somehow associated with the argument passed to the function, and any modification on their corresponding local variables within the function are reflected in the variables passed as arguments in the call.
In fact, a, b, and c become aliases of the arguments passed on the function call (x, y, and z) and any change on a within the function is actually modifying variable x outside the function. Any change on b modifies y, and any change on c modifies z. That is why when, in the example, function duplicate modifies the values of variables a, b, and c, the values of x, y, and z are affected.
If instead of defining duplicate as:

Was it to be defined without the ampersand signs as:
The variables would not be passed by reference, but by value, creating instead copies of their values. In this case, the output of the program would have been the values of x, y, and z without being modified (i.e., 1, 3, and 7).

Efficiency considerations and const references

Calling a function with parameters taken by value causes copies of the values to be made. This is a relatively inexpensive operation for fundamental types such as int, but if the parameter is of a large compound type, it may result on certain overhead. For example, consider the following function:

This function takes two strings as parameters (by value), and returns the result of concatenating them. By passing the arguments by value, the function forces a and b to be copies of the arguments passed to the function when it is called. And if these are long strings, it may mean copying large quantities of data just for the function call.
But this copy can be avoided altogether if both parameters are made references:
Arguments by reference do not require a copy. The function operates directly on (aliases of) the strings passed as arguments, and, at most, it might mean the transfer of certain pointers to the function. In this regard, the version of concatenate taking references is more efficient than the version taking values, since it does not need to copy expensive-to-copy strings.
On the flip side, functions with reference parameters are generally perceived as functions that modify the arguments passed, because that is why reference parameters are actually for.
The solution is for the function to guarantee that its reference parameters are not going to be modified by this function. This can be done by qualifying the parameters as constant:

By qualifying them as const, the function is forbidden to modify the values of neither a nor b, but can actually access their values as references (aliases of the arguments), without having to make actual copies of the strings.
Therefore, const references provide functionality similar to passing arguments by value, but with an increased efficiency for parameters of large types. That is why they are extremely popular in C++ for arguments of compound types. Note though, that for most fundamental types, there is no noticeable difference in efficiency, and in some cases, const references may even be less efficient!

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Inline functions

Calling a function generally causes a certain overhead (stacking arguments, jumps, etc...), and thus for very short functions, it may be more efficient to simply insert the code of the function where it is called, instead of performing the process of formally calling a function.
Preceding a function declaration with the inline specifier informs the compiler that inline expansion is preferred over the usual function call mechanism for a specific function. This does not change at all the behavior of a function, but is merely used to suggest the compiler that the code generated by the function body shall be inserted at each point the function is called, instead of being invoked with a regular function call.
For example, the concatenate function above may be declared inline as:
This informs the compiler that when concatenate is called, the program prefers the function to be expanded inline, instead of performing a regular call. inline is only specified in the function declaration, not when it is called.
Note that most compilers already optimize code to generate inline functions when they see an opportunity to improve efficiency, even if not explicitly marked with the inline specifier. Therefore, this specifier merely indicates the compiler that inline is preferred for this function, although the compiler is free to not inline it, and optimize otherwise. In C++, optimization is a task delegated to the compiler, which is free to generate any code for as long as the resulting behavior is the one specified by the code.

Default values in parameters

In C++, functions can also have optional parameters, for which no arguments are required in the call, in such a way that, for example, a function with three parameters may be called with only two. For this, the function shall include a default value for its last parameter, which is used by the function when called with fewer arguments. For example:

In this example, there are two calls to function divide. In the first one:
The call only passes one argument to the function, even though the function has two parameters. In this case, the function assumes the second parameter to be 2 (notice the function definition, which declares its second parameter as int b=2). Therefore, the result is 6.
In the second call:

The call passes two arguments to the function. Therefore, the default value for b (int b=2) is ignored, and b takes the value passed as argument, that is 4, yielding a result of 5.

Declaring functions

In C++, identifiers can only be used in expressions once they have been declared. For example, some variable x cannot be used before being declared with a statement, such as:
The same applies to functions. Functions cannot be called before they are declared. That is why, in all the previous examples of functions, the functions were always defined before the main function, which is the function from where the other functions were called. If main were defined before the other functions, this would break the rule that functions shall be declared before being used, and thus would not compile.
The prototype of a function can be declared without actually defining the function completely, giving just enough details to allow the types involved in a function call to be known. Naturally, the function shall be defined somewhere else, like later in the code. But at least, once declared like this, it can already be called.
The declaration shall include all types involved (the return type and the type of its arguments), using the same syntax as used in the definition of the function, but replacing the body of the function (the block of statements) with an ending semicolon.
The parameter list does not need to include the parameter names, but only their types. Parameter names can nevertheless be specified, but they are optional, and do not need to necessarily match those in the function definition. For example, a function called protofunction with two int parameters can be declared with either of these statements:

Anyway, including a name for each parameter always improves legibility of the declaration.
This example is indeed not an example of efficiency. You can probably write yourself a version of this program with half the lines of code. Anyway, this example illustrates how functions can be declared before its definition:
The following lines:

Declare the prototype of the functions. They already contain all what is necessary to call them, their name, the types of their argument, and their return type (void in this case). With these prototype declarations in place, they can be called before they are entirely defined, allowing for example, to place the function from where they are called (main) before the actual definition of these functions.
But declaring functions before being defined is not only useful to reorganize the order of functions within the code. In some cases, such as in this particular case, at least one of the declarations is required, because odd and even are mutually called; there is a call to even in odd and a call to odd in even. And, therefore, there is no way to structure the code so that odd is defined before even, and even before odd.

Recursivity

Recursivity is the property that functions have to be called by themselves. It is useful for some tasks, such as sorting elements, or calculating the factorial of numbers. For example, in order to obtain the factorial of a number (n!) the mathematical formula would be:
n! = n * (n-1) * (n-2) * (n-3) ... * 1
More concretely, 5! (factorial of 5) would be:
5! = 5 * 4 * 3 * 2 * 1 = 120
And a recursive function to calculate this in C++ could be:
Notice how in function factorial we included a call to itself, but only if the argument passed was greater than 1, since, otherwise, the function would perform an infinite recursive loop, in which once it arrived to 0, it would continue multiplying by all the negative numbers (probably provoking a stack overflow at some point during runtime).

Previous: Statements and flow control

Index

Next: Overloads and templates

C++ Standard Library
Containers
C standard library
Miscellaneous headers: <assert.h> <errno.h> <setjmp.h> <stdarg.h>

In the C++ programming language, the C++ Standard Library is a collection of classes and functions, which are written in the core language and part of the C++ ISO Standard itself.^[1]

Overview[edit]

The C++ Standard Library provides several generic containers, functions to utilize and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for everyday tasks such as finding the square root of a number. The C++ Standard Library also incorporates 18 headers of the ISO C90C standard library ending with '.h', but their use is deprecated.^[2] No other headers in the C++ Standard Library end in '.h'. Features of the C++ Standard Library are declared within the stdnamespace.

The C++ Standard Library is based upon conventions introduced by the Standard Template Library (STL), and has been influenced by research in generic programming and developers of the STL such as Alexander Stepanov and Meng Lee.^[3][4] Although the C++ Standard Library and the STL share many features, neither is a strict superset of the other.

A noteworthy feature of the C++ Standard Library is that it not only specifies the syntax and semantics of generic algorithms, but also places requirements on their performance.^[5] These performance requirements often correspond to a well-known algorithm, which is expected but not required to be used. In most cases this requires linear time O(n) or linearithmic time O(n log n), but in some cases higher bounds are allowed, such as quasilinear time O(n log²n) for stable sort (to allow in-place merge sort). Previously, sorting was only required to take O(n log n) on average, allowing the use of quicksort, which is fast in practice but has poor worst-case performance, but introsort was introduced to allow both fast average performance and optimal worst-case complexity, and as of C++11, sorting is guaranteed to be at worst linearithmic. In other cases requirements remain laxer, such as selection, which is only required to be linear on average (as in quickselect),^[6] not requiring worst-case linear as in introselect.

The C++ Standard Library underwent ISO standardization as part of the C++ ISO Standardization effort, and is undergoing further work^[7] regarding standardization of expanded functionality.

Implementations[edit]

At CppCon 2019 on September 16th, 2019, Microsoft announced releasing their implementation of the C++ Standard Library (also known as the STL) as open source.^[8] It is hosted on GitHub and licensed under the Apache License 2.0 with LLVM Exception.^[9][10]

The Apache C++ Standard Library is another open source implementation. It was originally developed commercially by Rogue Wave Software and later donated to the Apache Software Foundation.^[11] However, after more than five years without a release, the board of the Apache Software Foundation decided to end this project and move it to Apache Attic.^[12]

Standard headers[edit]

The following files contain the declarations of the C++ Standard Library.

Containers[edit]

<array>

New in C++11 and TR1. Provides the container class template std::array, a container for a fixed sized array.

<bitset>

Provides the specialized container class std::bitset, a bit array.

<deque>

Provides the container class template std::deque, a double-ended queue.

<forward_list>

New in C++11 and TR1. Provides the container class template std::forward_list, a singly linked list.

<list>

Provides the container class template std::list, a doubly linked list.

<map>

Provides the container class templates std::map and std::multimap, sorted associative array and multimap.

<queue>

Provides the container adapter class std::queue, a single-ended queue, and std::priority_queue, a priority queue.

<set>

Provides the container class templates std::set and std::multiset, sorted associative containers or sets.

<stack>

Provides the container adapter class std::stack, a stack.

<unordered_map>

New in C++11 and TR1. Provides the container class template std::unordered_map and std::unordered_multimap, hash tables.

<unordered_set>

New in C++11 and TR1. Provides the container class template std::unordered_set and std::unordered_multiset.

<vector>

Provides the container class template std::vector, a dynamic array.

General[edit]

<algorithm>

Provides definitions of many container algorithms.

<chrono>

Provides time elements, such as std::chrono::duration, std::chrono::time_point, and clocks.

Dev C++ Parts And Functions List

<functional>

Provides several function objects, designed for use with the standard algorithms.

<iterator>

Provides classes and templates for working with iterators.

Dev C++ Parts And Functions Pdf

<memory>

Provides facilities for memory management in C++, including the class template std::unique_ptr.

<stdexcept>

Contains standard exception classes such as std::logic_error and std::runtime_error, both derived from std::exception.

<tuple>

New in C++11 and TR1. Provides a class template std::tuple, a tuple.

<utility>

Provides the template class std::pair, for working with object pairs (two-member tuples), and the namespace std::rel_ops, for easier operator overloading.

Localization[edit]

<locale>

Defines classes and declares functions that encapsulate and manipulate the information peculiar to a locale.

<codecvt>

Provides code conversion facets for various character encodings.

Strings[edit]

<string>

Provides the C++ standard string classes and templates.

<regex>

New in C++11. Provides utilities for pattern matching strings using regular expressions.

Streams and input/output[edit]

<fstream>

Provides facilities for file-based input and output. See fstream.

<iomanip>

Provides facilities to manipulate output formatting, such as the base used when formatting integers and the precision of floating point values.

<ios>

Provides several types and functions basic to the operation of iostreams.

<iosfwd>

Provides forward declarations of several I/O-related class templates.

<iostream>

Provides C++ input and output fundamentals. See iostream.

<istream>

Provides the template class std::istream and other supporting classes for input.

<ostream>

Provides the template class std::ostream and other supporting classes for output.

<sstream>

Provides the template class std::stringstream and other supporting classes for string manipulation.

<streambuf>

Provides reading and writing functionality to/from certain types of character sequences, such as external files or strings.

Language support[edit]

<exception>

Provides several types and functions related to exception handling, including std::exception, the base class of all exceptions thrown by the Standard Library.

<limits>

Provides the template class std::numeric_limits, used for describing properties of fundamental numeric types.

<new>

Provides operators new and delete and other functions and types composing the fundamentals of C++ memory management.

<typeinfo>

Provides facilities for working with C++ run-time type information.

Dev C++ Parts And Functions Diagram

Thread support library[edit]

<thread>

New in C++11. Provide class and namespace for working with threads.

<mutex>

New in C++11. 30.4-1. This section provides mechanisms for mutual exclusion: mutexes, locks, and call once.

<condition_variable>

New in C++11. 30.5-1. Condition variables provide synchronization primitives used to block a thread until notified by some other thread that some condition is met or until a system time is reached.

<future>

New in C++11. 30.6.1-1. Describes components that a C++ program can use to retrieve in one thread the result (value or exception) from a function that has run in the same thread or another thread.

Numerics library[edit]

Components that C++ programs may use to perform seminumerical operations.

<complex>

The header <complex> defines a class template, and numerous functions for representing and manipulating complex numbers.

<random>

Facility for generating (pseudo-)random numbers

<valarray>

Defines five class templates (valarray, slice_array, gslice_array, mask_array, and indirect_array), two classes (slice and gslice),and a series of related function templates for representing and manipulating arrays of values.

<numeric>

Generalized numeric operations.

C standard library[edit]

Each header from the C Standard Library is included in the C++ Standard Library under a different name, generated by removing the .h, and adding a 'c' at the start; for example, 'time.h' becomes 'ctime'. The only difference between these headers and the traditional C Standard Library headers is that where possible the functions should be placed into the std:: namespace. In ISO C, functions in the standard library are allowed to be implemented by macros, which is not allowed by ISO C++.

See also[edit]

References[edit]

1. ^ISO/IEC 14882:2003(E) Programming Languages — C++ §17-27
2. ^ISO/IEC 14882:2003(E) Programming Languages — C++ §D.5
3. ^Bjarne Stroustrup. The Design and Evolution of C++ §8.5. Addison Wesley. ISBN0-201-54330-3.
4. ^Alexander Stepanov, Meng Lee (1 August 1994). 'The Standard Template Library'. HP Labs. Retrieved 22 October 2017.
5. ^'Generic Algorithms', David Musser
6. ^'std::nth_element'. cppreference.com. Retrieved 20 March 2018.
7. ^'JTC1/SC22/WG21 - The C++ Standards Committee'. ISO/IEC. Retrieved 7 July 2009.
8. ^https://devblogs.microsoft.com/cppblog/open-sourcing-msvcs-stl/
9. ^https://github.com/microsoft/STL
10. ^https://github.com/microsoft/STL/blob/master/LICENSE.txt
11. ^Apache C++ Standard Library
12. ^Brett Porter (18 July 2013). 'Apache C++ Standard Library and the Attic'. stdcxx-dev mailing list. Retrieved 27 February 2014.

Further reading[edit]

• Stroustrup, Bjarne. The C++ Programming Language. Addison-Wesley. ISBN978-0321563842.
• Josuttis, Nicolai. The C++ Standard Library - A Tutorial and Reference. Addison-Wesley. ISBN978-0-321-62321-8.
• Van Weert, Peter; Gregoire, Marc. C++ Standard Library Quick Reference. Apress. ISBN978-1484218754.

External links[edit]

• Apache C++ Standard Library Wiki, retired 15 May 2014 (based on Rogue Wave C++ Standard Library 4.1.0)