#line -- Preprocessing Directive

Reset line number
#line number newline
#line number filename newline
#line macros newline

#line is  a preprocessing  directive that resets  the line number  within a
file.  The  ANSI Standard defines  the line number  as being the  number of
newline characters read, plus one.

#line can  take any of  three forms.  The  first, #line number,  resets the
current line number in the source  file to number. The second, #line number
filename, resets the line number to number and changes the name of the file
to  filename.  The third,  #line  macros, contains  macros  that have  been
defined  by earlier  preprocessing directives.  When  the macros  have been
expanded by the preprocessor,  the #line instruction will then resemble one
of the first two forms and be interpreted appropriately.

See Also

C preprocessor
ANSI Standard, §6.8.4

Notes

Most  often, #line  is used  to  ensure that  error messages  point to  the
correct line  in the  program's source code.   A program generator  may use
this directive  to associate errors  in generated C code  with the original
sources.  For  example, the program generator  yacc uses #line instructions
to  link  the  C code  it  generates  with the  yacc  code  written by  the
programmer.

© 2012 by Stephen A. Ness