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Diffstat (limited to 'gcc/cpp.texi')
| -rw-r--r-- | gcc/cpp.texi | 26 |
1 files changed, 24 insertions, 2 deletions
diff --git a/gcc/cpp.texi b/gcc/cpp.texi index e9a9095..5751722 100644 --- a/gcc/cpp.texi +++ b/gcc/cpp.texi @@ -551,6 +551,7 @@ in the C preprocessor. * Concatenation:: Building tokens from parts taken from macro arguments. * Undefining:: Cancelling a macro's definition. * Redefining:: Changing a macro's definition. +* Poisoning:: Ensuring a macro is never defined or used. * Macro Pitfalls:: Macros can confuse the unwary. Here we explain several common problems and strange features. @end menu @@ -1370,7 +1371,7 @@ The same form of @samp{#undef} directive will cancel definitions with arguments or definitions that don't expect arguments. The @samp{#undef} directive has no effect when used on a name not currently defined as a macro. -@node Redefining, Macro Pitfalls, Undefining, Macros +@node Redefining, Poisoning, Undefining, Macros @subsection Redefining Macros @cindex redefining macros @@ -1404,7 +1405,28 @@ where there was no whitespace at all. Recall that a comment counts as whitespace. -@node Macro Pitfalls,, Redefining, Macros +@node Poisoning, Macro Pitfalls, Redefining, Macros +@subsection Poisoning Macros +@cindex poisoning macros + +Sometimes, there is an identifier that you want to remove completely +from your program, and make sure that it never creeps back in. To +enforce this, the @samp{#pragma poison} directive can be used. +@samp{#pragma poison} is followed by a list of identifiers to poison, +and takes effect for the rest of the source. You cannot @samp{#undef} a +poisoned identifier or test to see if it's defined with @samp{#ifdef}. + +For example, + +@example +#pragma poison printf sprintf fprintf +sprintf(some_string, "hello"); +@end example + +@noindent +will produce an error. + +@node Macro Pitfalls,, Poisoning, Macros @subsection Pitfalls and Subtleties of Macros @cindex problems with macros @cindex pitfalls of macros |