C++ examples for Preprocessor:Directive
There are several standard predefined preprocessing macros and the most useful are listed in the following Table.
Macro | Description |
---|---|
__LINE__ | The line number of the current source line as a decimal integer literal. |
__FILE__ | The name of the source file as a character string literal. |
__DATE__ | The date when the source file was processed as a character string literal in the form Mmm dd yyyy. Here, |
__TIME__ | The time at which the source file was compiled, as a character string literal in the form hh:mm:ss, |
You can modify the __LINE__ current line number using the #line directive and subsequent line numbers will increment from that.
For example, to start line numbering at 1000 you would add this directive:
#line 1000
You can use the #line directive to change the string returned by the __FILE__ macro.
Here's an example:
#line 1000 "The program file"
To alter the apparent file name and leave the line numbers unaltered, you could use the __LINE__ macro in the #line directive:
#line __LINE__ "The program file"
You can use the date and time macros to tell when your program was last compiled:
std::cout << "Program last compiled at " << __TIME__ << " on "<< __DATE__ << std::endl;