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

[edit]Syntax

[edit]Explanation

1) Changes the current preprocessor line number tolineno. Expansions of the macro__LINE__ beyond this point will expand tolineno plus the number of actual source code lines encountered since.

2) Also changes the current preprocessor file name tofilename. Expansions of the macro__FILE__ from this point will producefilename.

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 with0).

Iflineno is0 or greater than32767(until C++11)2147483647(since C++11), the behavior is undefined.

[edit]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.

[edit]Example

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

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

[edit]References

[edit]See also

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