c - 字符常量中的多个字符

Question

Some C compilers permit multiple characters in a character constant. This means that writing 'yes' instead of "yes" may well go undetected. Source: C traps and pitfalls

任何人都可以举一个字符常量中允许多个字符的例子吗？

Answer 1

正如 Code Monkey 所引用的那样，它是由实现定义的并且实现各不相同——这不仅仅是 BigEndian/LittleEndian 和字符集的差异。我已经用程序测试了四种实现(全部使用 ASCII)

#include <stdio.h>

int main()
{
    unsigned value = 'ABCD';
    char* ptr = (char*)&value;

    printf("'ABCD' = %02x%02x%02x%02x = %08x\n", ptr[0], ptr[1], ptr[2], ptr[3], value);
    value = 'ABC';
    printf("'ABC'  = %02x%02x%02x%02x = %08x\n", ptr[0], ptr[1], ptr[2], ptr[3], value);
    return 0;
}

我得到了四个不同的结果

大端(AIX、POWER、IBM 编译器)

'ABCD' = 41424344 = 41424344
'ABC'  = 00414243 = 00414243

大端(Solaris、Sparc、SUN 编译器)

'ABCD' = 44434241 = 44434241
'ABC'  = 00434241 = 00434241

小端(Linux、x86_64、gcc)

'ABCD' = 44434241 = 41424344
'ABC'  = 43424100 = 00414243

小端(Solaris、x86_64、Sun 编译器)

'ABCD' = 41424344 = 44434241
'ABC'  = 41424300 = 00434241