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

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

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)

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

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