__BUILTIN_TYPES_COMPATIBLE_P函数

__BUILTIN_TYPES_COMPATIBLE_P

名字：
__builtin_types_compatible_p GNU扩展，用来判断两个类型是否相同

原型

int 
__builtin_types_compatible_p(type_a, type_b);

描述：
此函数为GNU扩展，用来判断两个类型是否相同，如果type_a与 type_b相同的话，就会返回1，否则的话，返回0。

请注意一下情景：

两个类型的sizeof值跟它的类型判断是相互不影响的，例如：在i386架构下，sizeof(char *) 和 sizeof(int) 的值是相同的，但是他们的类型却是不相同的。
限定符会被忽略，例如const long和long他们的类型是相同的。
相同的类型不同的指针级数是不相同的例如：double*和double**是不相同的。
连个用typedef定义的类型，当且进档他们定义的类型是相同的时候，=它们是相同的。
enum类型是一种特殊的情况，两个enum类型是不相同的。

原文


__BUILTIN_TYPES_COMPATIBLE_P(3)     Library Functions Manual

NAME
     __builtin_types_compatible_p - GNU extension to check equivalent types

SYNOPSIS
     int
     __builtin_types_compatible_p(type_a, type_b);

DESCRIPTION
     The __builtin_types_compatible_p() is a GNU extension for determining whether two types are equivalent.  
     If type_a is equivalent to type_b, a value 1 is returned.  Otherwise __builtin_types_compatible_p() returns 0.

    The following remarks should be taken into account.
    1.The architecture-specific size of the two types does not have an impact on the result. 
    For example, sizeof(char *) and sizeof(int) result the same value on i386, but the types naturally are not equivalent.
    2.Type qualifiers are ignored.  The function returns the same value for long and const long.
    3. The amount of pointer indirection affects the result.  For example, double * is not equivalent to double **.
    4.Two types defined with typedef are equivalent if and only if their underlying types are equivalent.
    5. The enum type is a special case in that two enum types are not considered equivalent.

EXAMPLES
    The following example combines __builtin_types_compatible_p() and the typeof(3) construct:
   #define __COMPARE_TYPES(v, t)      \
        __builtin_types_compatible_p(__typeof__(v), t)
    ...
    if (__COMPARE_TYPES(p, double) != 0)
                   err(EX_DATAERR, "invalid type");

SEE ALSO
     gcc(1), __builtin_constant_p(3), typeof(3)

CAVEATS
     This is a non-standard, compiler-specific extension.
NetBSD 7.99   December 21, 2010

__BUILTIN_TYPES_COMPATIBLE_P函数

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