Filename and line information

Changes the source code's line number and, optionally, the current file name, in the preprocessor.

Syntax

Explanation

1) Changes the current preprocessor line number to lineno . Expansions of the macro __LINE__ beyond this point will expand to lineno plus the number of actual source code lines encountered since.

2) Also changes the current preprocessor file name to filename . Expansions of the macro __FILE__ from this point will produce filename .

Any preprocessing tokens (macro constants or expressions) are permitted as arguments to #line as long as they expand to a valid decimal integer optionally following a valid character string.

lineno must be a sequence of at least one decimal digit (the program is ill-formed, otherwise) and is always interpreted as decimal (even if it starts with 0 ).

If lineno is 0 or greater than 32767 (until C++11) 2147483647 (since C++11) , the behavior is undefined.

Notes

This directive is used by some automatic code generation tools which produce C++ source files from a file written in another language. In that case, #line directives may be inserted in the generated C++ file referencing line numbers and the file name of the original (human-editable) source file.

Example

#include <cassert>
#define FNAME "test.cc"
int main()
{
#line 777 FNAME
        assert(2+2 == 5);
}

test: test.cc:777: int main(): Assertion `2+2 == 5' failed.

References

See also