I hava a look at many header files they have codes like #ifndef and #endif
what does they explain,please.
smdjilani 0 js
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Jump to PostThe #ifndef is used for checking if the macro is not already defined, if macro is defined already it will do nothing, if not we can define macro.
below example should clarify your doubt.
to see effect uncomment #define MAX 5#include <stdio.h> //#define MAX 5 #ifndef …
All 3 Replies
clife 0 Unverified User
The #ifndef is used for checking if the macro is not already defined, if macro is defined already it will do nothing, if not we can define macro.
below example should clarify your doubt.
to see effect uncomment #define MAX 5
#include <stdio.h>
//#define MAX 5
#ifndef MAX
#define MAX 10
#endif
int main()
{
int cnt = 1 ;
for(; cnt <= MAX; cnt++)
printf("%d Hello\n",cnt);
return 0;
}
deceptikon 1,790 Code Sniper Team Colleague Featured Poster
To add to clife's explanantion, #ifndef foo is functionally identical to #if !defined(foo).
rubberman 1,355 Nearly a Posting Virtuoso Featured Poster
#ifndef is also frequently used to "guard" header files from being included multiple times, which can be a real problem. Example (myheader.h):
#ifndef MY_HEADER_H
#define MY_HEADER_H
.
.
.
#endif /* MY_HEADER_H */
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