为什么* P ++从* P + = 1有什么不同？ [英] Why is *p++ different from *p += 1?

问题描述

考虑：

void foo1(char **p) { *p++; }
void foo2(char **p) { *p += 1; }

和

char *s = "abcd";
char *a = s; 
foo1(&a); 
printf("%s", a); //abcd

但如果我用 foo2的（）而不是：

char *a = s; 
foo2(&a); 
printf("%s", a); //bcd

有人能解释一下吗？

Can someone explain it?

推荐答案

关键是的precedence的 + = 和 ++ 运营商。在 ++ 具有更高的precedence比 + = （事实​​上，赋值运算符有第二低$中的p C $ pcedence），所以操作

The key is the precedence of the += and the ++ operator. The ++ has a higher precedence than the += (in fact, assignment operators have the second lowest precedence in C), so the operation

*p++

意味着取消引用指针，然后递增指针的本身按1（如通常，根据指针运算规则，它不一定是一个字节，而的sizeof（ * p）有关结果地址）。另一方面，

means dereference the pointer, then increment the pointer itself by 1 (as usually, according to the rules of pointer arithmetic, it's not necessarily one byte, but rather sizeof(*p) regarding the resulting address). On the other hand,

*p += 1

办法增加值的指向指针一（什么都不做与指针本身）。

means increment the value pointed to by the pointer by one (and do nothing with the pointer itself).

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