GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic. For example, a project’s policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings. Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.
#pragma GCC diagnostic kind option
Modifies the disposition of a diagnostic. Note that not all diagnostics are modifiable; at the moment only warnings (normally controlled by ‘-W…’) can be controlled, and not all of them. Use -fdiagnostics-show-option to determine which diagnostics are controllable and which option controls them.
kind is ‘error’ to treat this diagnostic as an error, ‘warning’ to treat it like a warning (even if -Werror is in effect), or ‘ignored’ if the diagnostic is to be ignored. option is a double quoted string that matches the command-line option.
#pragma GCC diagnostic warning "-Wformat" #pragma GCC diagnostic error "-Wformat" #pragma GCC diagnostic ignored "-Wformat"
Note that these pragmas override any command-line options. GCC keeps track of the location of each pragma, and issues diagnostics according to the state as of that point in the source file. Thus, pragmas occurring after a line do not affect diagnostics caused by that line.
#pragma GCC diagnostic push
#pragma GCC diagnostic pop
Causes GCC to remember the state of the diagnostics as of each
push, and restore to that point at each
pop. If a
pop has no matching
push, the command-line options are
#pragma GCC diagnostic error "-Wuninitialized" foo(a); /* error is given for this one */ #pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wuninitialized" foo(b); /* no diagnostic for this one */ #pragma GCC diagnostic pop foo(c); /* error is given for this one */ #pragma GCC diagnostic pop foo(d); /* depends on command-line options */
GCC also offers a simple mechanism for printing messages during compilation.
#pragma message string
Prints string as a compiler message on compilation. The message is informational only, and is neither a compilation warning nor an error.
#pragma message "Compiling " __FILE__ "..."
string may be parenthesized, and is printed with location information. For example,
#define DO_PRAGMA(x) _Pragma (#x) #define TODO(x) DO_PRAGMA(message ("TODO - " #x)) TODO(Remember to fix this)
prints ‘/tmp/file.c:4: note: #pragma message: TODO - Remember to fix this’.