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(C++23)(C++23) | ||||
(C++17) | ||||
(C++23) | ||||
(C++11) | ||||
#line | ||||
(C++26) |
Changes the source code's line number and, optionally, the current file name, in the preprocessor.
Contents |
#linelineno | (1) | ||||||||
#linelineno"filename" | (2) | ||||||||
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.
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.
#include <cassert>#define FNAME "test.cc"int main(){#line 777 FNAMEassert(2+2==5);}
Possible output:
test: test.cc:777: int main(): Assertion `2+2 == 5' failed.
(C++20) | a class representing information about the source code, such as file names, line numbers, and function names (class)[edit] |
C documentation forFilename and line information | |
