C macros _ line __, _ file _ and _ FUNC __

It is possible for a C program to print the currently executing line of source code, the file of the source code, and the name of the current function. the currently executing line is available in a Preprocessor variable called__LINE__:

#include <stdio.h>int main (){    printf ("This is line %d.\n", __LINE__);    return 0;}

This prints out

This is line 5.

To get the name of the file, use the Preprocessor variable__FILE__:

#include <stdio.h>int main (){    printf ("This is line %d of file \"%s\".\n",            __LINE__, __FILE__);    return 0;}

This prints out

This is line 6 of file "/share/websites/www.lemoda.net/c/line-file-func/file.c".

C99 (the most recent version of the C language, at the time of writing) introduced another macro called__func__Which also names the function in use:

#include <stdio.h>#define BLURT printf ("This is line %d of file %s (function %s)\n",\                      __LINE__, __FILE__, __func__)void silly_function (){    BLURT;}int main (){    BLURT;    silly_function ();    return 0;}

This prints out

This is line 13 of file /share/websites/www.lemoda.net/c/line-file-func/func.c (function main)This is line 8 of file /share/websites/www.lemoda.net/c/line-file-func/func.c (function silly_function)

You can change the values used__FILE__And__LINE__Using a line directive, which is a Preprocessor command of the form

#line 20 "some-file"

Which tells the C compiler that the next line after the line directive is line 20some-file.

#include <stdio.h>#define BLURT printf ("This is line %d of file \"%s\" (function <%s>)\n",\                      __LINE__, __FILE__, __func__)#line 99 "grody-to-the-max"void silly_function (){    BLURT;}#line 999 "bassetts-liquorice-allsorts"int main (){    BLURT;    silly_function ();    return 0;}

This prints out

This is line 1001 of file "bassetts-liquorice-allsorts" (function <main>)This is line 101 of file "grody-to-the-max" (function <silly_function>)

This line directive is used by facilities like "Lex" and "YACC" which output C code so that error messages are related to the input file rather than the Output C file.

GCC (the "GNU Compiler Collection") also defines__FUNCTION__And__PRETTY_FUNCTION__. These are both the same
__func__For C. For C ++,__PRETTY_FUNCTION__Is something different.

It is possible for a C program to print the currently executing line of source code, the file of the source code, and the name of the current function. the currently executing line is available in a Preprocessor variable called__LINE__:

#include <stdio.h>int main (){    printf ("This is line %d.\n", __LINE__);    return 0;}

This prints out

This is line 5.

To get the name of the file, use the Preprocessor variable__FILE__:

#include <stdio.h>int main (){    printf ("This is line %d of file \"%s\".\n",            __LINE__, __FILE__);    return 0;}

This prints out

This is line 6 of file "/share/websites/www.lemoda.net/c/line-file-func/file.c".

C99 (the most recent version of the C language, at the time of writing) introduced another macro called__func__Which also names the function in use:

#include <stdio.h>#define BLURT printf ("This is line %d of file %s (function %s)\n",\                      __LINE__, __FILE__, __func__)void silly_function (){    BLURT;}int main (){    BLURT;    silly_function ();    return 0;}

This prints out

This is line 13 of file /share/websites/www.lemoda.net/c/line-file-func/func.c (function main)This is line 8 of file /share/websites/www.lemoda.net/c/line-file-func/func.c (function silly_function)

You can change the values used__FILE__And__LINE__Using a line directive, which is a Preprocessor command of the form

#line 20 "some-file"

Which tells the C compiler that the next line after the line directive is line 20some-file.

#include <stdio.h>#define BLURT printf ("This is line %d of file \"%s\" (function <%s>)\n",\                      __LINE__, __FILE__, __func__)#line 99 "grody-to-the-max"void silly_function (){    BLURT;}#line 999 "bassetts-liquorice-allsorts"int main (){    BLURT;    silly_function ();    return 0;}

This prints out

This is line 1001 of file "bassetts-liquorice-allsorts" (function <main>)This is line 101 of file "grody-to-the-max" (function <silly_function>)

This line directive is used by facilities like "Lex" and "YACC" which output C code so that error messages are related to the input file rather than the Output C file.

GCC (the "GNU Compiler Collection") also defines__FUNCTION__And__PRETTY_FUNCTION__. These are both the same
__func__For C. For C ++,__PRETTY_FUNCTION__Is something different.