Comments serve as a sort of in-code documentation. When inserted into a program, they are effectively ignored by the compiler; they are solely intended to be used as notes by the humans that read source code. Although specific documentation is not part of the C++ standard, several utilities exist that parse comments with different documentation formats.
Syntax
/* comment */ | (1) | |
// comment\n | (2) |
All comments are removed from the program at translation phase 3 by replacing each comment with a single whitespace character.
C-style
C-style comments are usually used to comment large blocks of text, however, they can be used to comment single lines. To insert a C-style comment, simply surround text with /*
and */
; this will cause the contents of the comment to be ignored by the compiler. Although it is not part of the C++ standard, /**
and */
are often used to indicate documentation blocks; this is legal because the second asterisk is simply treated as part of the comment. C-style comments cannot be nested.
C++-style
C++-style comments are usually used to comment single lines, however, multiple C++-style comments can be placed together to form multi-line comments. C++-style comments tell the compiler to ignore all content between //
and a new line.
Notes
Because comments are removed before the preprocessor stage, a macro cannot be used to form a comment and an unterminated C-style comment doesn't spill over from an #include'd file.
Besides commenting out, other mechanisms used for source code exclusion are.
#if 0 std::cout << "this will not be executed or even compiled\n"; #endif
and.
if(false) { std::cout << "this will not be executed\n" }
Example
/* C-style comments can contain multiple lines */ /* or just one */ // C++-style comments can comment one line // or, they can // be strung together int main() { // The below code won't be run // return 1; // The below code will be run return 0; }
See Also
C documentation for comment |
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