.CPP

Introduction

A .cpp file holds source code in C++, the language that grew out of C with classes, templates and a large standard library. As in C, a compiler turns each source file into an object file, and a linker joins them into a program or library.

Compilers do not agree on one extension, so several are common: .cpp, .cc and .cxx for source files, and .hpp, .hh, .hxx or plain .h for headers. Since C++20, modules may use extensions such as .cppm or .ixx, depending on the compiler.

Structure

A C++ source file is plain text with no header or signature. Like C, it first passes through the preprocessor, which handles #include, #define and #if lines. What remains is a series of declarations: namespaces, classes, templates, functions and variables. Headers hold the declarations that several source files share; templates are usually defined in full in headers, because the compiler needs their code wherever they are used.

#include <iostream>
#include <string>

int main()
{
    std::string name = "world";
    std::cout << "Hello, " << name << '\n';
}

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