可以在令牌粘贴之前扩展宏吗？

Question

请考虑以下代码：

#define TOTO 0xAA
#define TITI 0xBB

unsigned char val0xAA[] = {1, 2, 3};
unsigned char val0xBB[] = {4, 5, 6};

// Macro using Token pasting
#define VAL(_x_) val##_x_

void foo(void)
{
    // Silly attempt to abuse preprocessor
    unsigned char *tab1 = VAL(TOTO);
    unsigned char *tab2 = VAL(TITI);
}

我希望VAL(TOTO)宏扩展为val0xAA，但实际上会扩展为valTOTO并且编译失败。

问题是：在令牌粘贴评估之前，是否有可能“强制/优先”评估TOTO ？

Answer 1

是的，这是一个常见的伎俩。只需添加另一个图层。

#define TOTO 0xAA
#define TITI 0xBB

unsigned char val0xAA[] = {1, 2, 3};
unsigned char val0xBB[] = {4, 5, 6};

// Macro using Token pasting
#define VAL1(_x_) val##_x_
#define VAL(_x_) VAL1(_x_) // expand and pass to VAL1 to concatenate 

void foo(void)
{
    // Silly attempt to abuse preprocessor
    unsigned char *tab1 = VAL(TOTO);
    unsigned char *tab2 = VAL(TITI);
}