DIRECTIVEPublished

#ifndef

#ifndef <identificador> ... [#else ...] #endif

Includes a block only when a given identifier is not defined.

Compilação condicionalValores padrãoPré-processador

01 · OVERVIEW

Overview

#ifndef is the inverse of #ifdef. It is useful for header guards and defaults: the block remains only when the symbol does not exist at that preprocessing point.

02 · SYNTAX

Syntax

#ifndef <identificador> ... [#else ...] #endif

03 · PRACTICAL EXAMPLE

Protected default value

#ifndef BANCO_DADOS_PADRAO
    #define BANCO_DADOS_PADRAO "MSSQL"
#endif

User Function ExIfNDef()
    ConOut("Banco padrão: " + BANCO_DADOS_PADRAO)
Return

Expected result

MSSQL is defined only when no previous definition is active.

BEST PRACTICES

Use it to provide a default without overriding an earlier definition.
Always close with #endif.

COMMON PITFALLS

Changing a compiled default requires recompilation.
An undefined symbol is not the same as a false logical value.

#ifndef

Overview

Syntax

Protected default value

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