c:preprocessor:undef
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| + | ====== #undef ====== | ||
| + | |||
| + | ===== Description ===== | ||
| + | With the # undef a macro can be overridden.\\ | ||
| + | Status "defined" or "undefined" is an important characteristic of an identifier, regardless of its actual definition.\\ | ||
| + | The # ifdef and # ifndef can be used to check whether an identifier is currently defined or not.\\ | ||
| + | |||
| + | Syntax\\ | ||
| + | <code c> | ||
| + | #undef macro_name | ||
| + | </code> | ||
| + | |||
| + | ===== c undef example ===== | ||
| + | <code c> | ||
| + | #include <stdio.h> | ||
| + | |||
| + | int main(void) | ||
| + | { | ||
| + | #define TESTDEFINE 1 | ||
| + | printf("%d\n", TESTDEFINE); | ||
| + | |||
| + | #undef TESTDEFINE | ||
| + | |||
| + | #define TESTDEFINE 42 | ||
| + | printf("%d\n", TESTDEFINE); | ||
| + | |||
| + | return 0; | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | === output === | ||
| + | 1 | ||
| + | 42 | ||
on the occasion of the current invasion of Russia in Ukraine
c/preprocessor/undef.txt · Last modified: 2024/02/16 01:06 (external edit)
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