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C Language > Learn C Language > How can you check to see whether a symbol is defined?
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How can you check to see whether a symbol is defined?

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Professional Tutor with 15 years of experience.

You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
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Thank You for the question .... To check the symbol has been defined use the #ifdef function. Thank You, Team DishaaPro www.dishaapro.com
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Having 17 years of teaching experience

To check whether the symbol is defined or not you have to use #ifdef or #ifndef. You can check like a simple if condition: #ifdef NAME (the course of ation i.e. your c / c++ code) #else (the course of ation i.e. your c / c++ code) #endif
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You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
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Software Professional Trainer with 26+ years of Experience in Software Design and Development

#ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or (#ifndef). #ifndef OS #define OS unix #endif ========= #ifdef UNIX #define OS unix #else #define OS windows #endif
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Tutor

you can use #if def and #ifndef
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Trainer

You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
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You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined.
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defined where in what scope? And where do you want to check in the source code or object file or library or executable?
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Mathematics and Computer science guide

You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef). Many programmers like to ensure that their own version of NULL is defined, not someone else's. This task can be accomplished as shown here: #ifdef...
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You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef). Many programmers like to ensure that their own version of NULL is defined, not someone else's. This task can be accomplished as shown here: #ifdef NULL #undef NULL #endif #define NULL (void*) 0 The first line, #ifdef NULL, checks to see whether the NULL symbol has been defined. If so, it is undefined using #undef NULL and the new definition of NULL is defined. To check whether a symbol has not been defined yet, you would use the #ifndef preprocessor directive. read less
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