c - 做了一些指针数学但不起作用

Question

我正在尝试学习 c 语言中的指针，为此我重新设计了一个 for 循环以从末尾开始循环到开头。

int main(int argc, char* argv[]) {
    int ages[] = {23, 43, 12, 89, 2};
    char* names[] = {"Alan", "Frank", "Mary", "John", "Lisa"};

    // safely get the size of ages
    int count = sizeof(ages) / sizeof(int);
    int i = 0;

    int* cur_age = ages;
    char** cur_name = names;

    // This is the original for loop:
    for (cur_name = names, cur_age = ages; (cur_age - ages) < count;
         cur_name++, cur_age++) {
        printf("%s lived %d years so far.\n", *cur_name, *cur_age);
    }

    // This is my version:
    for (cur_name = names + (count - 1), cur_age = ages + (count - 1);
         cur_age == ages; cur_name--, cur_age--) {
        printf("%s lived %d years so far.\n", *cur_name, *cur_age);
    }

    // I added this line and observed that cur_name is always equal to names +
    // 32
    // for example names: 0x7fff55268250, cur_name: 0x7fff55268270
    printf(" names: %p, cur_name: %p\n", names, cur_name);
}

问题是我的 for 循环版本没有打印任何内容，尽管我观察到指针的初始化实际上正在改变它们的值。我已经检查了数学，但仍然无法弄清楚为什么这不起作用。任何启示都将不胜感激。

Answer 1

你的循环条件错误，应该是cur_age >= ages，而不是cur_age == ages。

按照您编写的方式，循环条件在第一次迭代时为 false，因此循环立即终止。