DEFINED

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgDefined
• Last revised: 2025-11-15

---

Preprocessor function to test if a symbol has been defined

Syntax

` defined (symbol_name)

`

Parameters

symbol_name

Name of the symbol to test

Return Value

Returns non-zero (-1) if the symbol has been defined, otherwise returns zero (0).

Description

Given the symbol name, the defined() preprocessor function returns true if the symbol has been defined - or false if the symbol is unknown.

This is used mainly with #if (or #elseif).

Similar to #ifdef (or #elseifdef) except it allows more than one check to occur because of its flexibility.

Examples

start GeSHi

'e.g. - which symbols are defined out of a, b, c, and d ?

Const a = 300
#define b 12
Dim c As Single

#if defined(a)
 Print "a is defined"
#endif
#if defined(b)
 Print "b is defined"
#endif
#if defined(c)
 Print "c is defined"
#endif
#if defined(d)
 Print "d is defined"
#endif

end GeSHi

Differences from QB

• New to FreeBASIC

See also

• #define
• #macro
• #if
• #else
• #elseif
• #elseifdef
• #elseifndef
• #endif
• #ifdef
• #ifndef
• #undef

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