Copyright (c) 2010 Jukka Ruohonen <jruohonen@iki.fi>
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.Dd December 21, 2010 .Dt __BUILTIN_TYPES_COMPATIBLE_P 3 .Os .Sh NAME .Nm __builtin_types_compatible_p .Nd GNU extension to check equivalent types .Sh SYNOPSIS .Ft int .Fn __builtin_types_compatible_p "type_a" "type_b" .Sh DESCRIPTION The .Fn __builtin_types_compatible_p is a .Tn GNU extension for determining whether two types are equivalent. If .Fa type_a is equivalent to .Fa type_b , a value 1 is returned. Otherwise .Fn __builtin_types_compatible_p returns 0.
p The following remarks should be taken into account. l -enum -offset indent t The architecture-specific size of the two types does not have an impact on the result. For example, .Fn sizeof "char *" and .Fn sizeof "int" result the same value on i386, but the types naturally are not equivalent. t Type qualifiers are ignored. The function returns the same value for .Vt long and .Vt const long . t The amount of pointer indirection affects the result. For example, .Vt double * is not equivalent to .Vt double ** . t Two types defined with .Em typedef are equivalent if and only if their underlying types are equivalent. t The .Em enum type is a special case in that two .Em enum types are not considered equivalent. .El .Sh EXAMPLES The following example combines .Fn __builtin_types_compatible_p and the .Xr typeof 3 construct: d -literal -offset indent #define __COMPARE_TYPES(v, t) \\ __builtin_types_compatible_p(__typeof__(v), t) ... if (__COMPARE_TYPES(p, double) != 0) err(EX_DATAERR, "invalid type"); .Ed .Sh SEE ALSO .Xr gcc 1 , .Xr __builtin_constant_p 3 , .Xr typeof 3 .Sh CAVEATS This is a non-standard, compiler-specific extension.