#line Directive
Preprocessor directive that sets the compiler's internally-stored line number and filename to the specified values.
| #line lineNumber "filename" |
|---|
Parameters
| Item | Description |
|---|---|
| lineNumber |
Line number to set. This can be any integer constant. Macro replacement can be performed on the preprocessing tokens, as long as the result evaluates to the correct syntax. |
| filename [optional] |
Filename to set. The filename can be any combination of characters, and must be enclosed in double quotation marks (" "). If this parameter is omitted, the previous filename remains unchanged. |
Remarks
The compiler uses the line number and filename to refer to errors that it finds during compilation. The line number usually refers to the current input line, and the filename refers to the current input file. The line number is incremented after each line is processed. If you change the line number and filename, the compiler ignores the previous values and continues processing with the new values. The #line directive is typically used by program generators to cause error messages to refer to the original source file instead of to the generated program.
The translator uses the line number and filename to determine the values of the predefined macros __FILE__ and __LINE__. You can use these macros to insert self-descriptive error messages into the program text. The __FILE__ macro expands to a string whose contents are the filename, surrounded by double quotation marks (" ").
Examples
The following example sets the line number to 151 and the filename to "copy.c".
#line 151 "copy.c"
In the following example, the macro ASSERT uses the predefined macros __LINE__ and __FILE__ to print an error message about the source file if the specified assertion is not true.
#define ASSERT(cond)
if( !(cond) )\
{printf( "assertion error line %d, file(%s)\n", \
__LINE__, __FILE__ );}