I see this in KR C programming language. I really did not understand what it means. If it is line number of current source then we could use __LINE__. But what is the use of #line actually?
johndoe444 1 Posting Whiz in Training
jephthah 1,888 Posting Maven
i never understood it either, as the more obscure commands in the C pre-processor are beyond the scope of my typical work.
that said, a good overview of the C pre-processor and descriptions of all the commands in the processing language can be found at http://gcc.gnu.org/onlinedocs/cpp/index.html#Top .. line control has its own section
Ancient Dragon 5,243 Achieved Level 70 Team Colleague Featured Poster
In order for the compiler to produce meaningful references to line numbers in preprocessed source, the preprocessor inserts #line directives where necessary (for example, at the beginning and after the end of included text).
When the preprocessor parses your *.c program it will create a *.i file that expands all the #include and other preprocessor statements. In doing that all the include files are merged into one *.i file. When doing that it adds the #line directives so that it can keep track of the line numbers from the original file. Then when the compiler compiles the *.i file it will know the line numbers from the original files and use them to produce meaningful error messages. Without #line directives you would get line numbers from the *.i file, not the *.c or *.h file that you wrote.
I know of no reason why a programmer would want to insert #line directives in his program.
jephthah commented: thanks for parsing that. +7
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