General form of #line preprocessor is #line number "filename"

Here the file name is optional. Filename string replaces the string value of _ _FILE_ _ while the number changes the value of _ _LINE_ _.

The major use of #line is in debugging and rare programming situation.

Following C Source code shows the #line preprocessor in action -

#include

int main ()

{

printf ("n%d", __LINE__); //Prints 6

#line 100;

printf ("n%d",__LINE__); // Prints 101

printf ("n%d", __FILE__);// Prints original source file name

#line 103 "Super C"

printf ("n%d", __FILE__); //Prints Super C

return 0;

}