DIRECTIVEPublished

#undef

#undef <identificador>

Removes an active definition from the point where the directive appears.

Pré-processadorConstantesEscopo lexical

01 · OVERVIEW

Overview

#undef cancels an identifier previously created by #define. After it, #ifdef no longer sees the symbol as defined, and the same name may be defined again.

02 · SYNTAX

Syntax

#undef <identificador>

03 · PRACTICAL EXAMPLE

Temporary symbol

#define MODO_TESTE

#ifdef MODO_TESTE
    #define PREFIXO_LOG "[TESTE] "
#endif

#undef MODO_TESTE

User Function ExUndef()
#ifdef MODO_TESTE
    ConOut("Este trecho não será compilado")
#endif
Return

Expected result

After #undef, the following conditional block is discarded.

BEST PRACTICES

Use #undef when a symbol is needed in only part of a source unit.
Removal affects only lines processed after the directive.

COMMON PITFALLS

#undef does not free runtime memory because the definition was not a variable.
Repeated redefinitions reduce readability.

#undef

Overview

Syntax

Temporary symbol

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