通过指针从 C 和 C++ 中的函数返回本地数据 [英] Returning local data from functions in C and C++ via pointer

问题描述

我和朋友吵架了.他说我可以从函数返回一个指向本地数据的指针.这不是我学到的，但我找不到反驳他来证明我的知识.

I have argument with my friend. He says that I can return a pointer to local data from a function. This is not what I have learned but I can't find a counterargument for him to prove my knowledge.

以下是图例:

char *name() {
    char n[10] = "bodacydo!";
    return n;
}

它被用作:

int main() {
    char *n = name();
    printf("%s
", n);
}

他说这完全没问题，因为在程序调用 name 后，它返回一个指向 n 的指针，然后就在此之后打印它.同时程序中没有其他任何事情发生，因为它是单线程的并且是串行执行的.

He says this is perfectly OK because after a program calls name, it returns a pointer to n, and right after that it just prints it. Nothing else happens in the program meanwhile, because it's single threaded and execution is serial.

我找不到反驳的论点.我永远不会写那样的代码，但他很固执，说这完全没问题.如果我是他的老板，我会因为他是一个顽固的白痴而解雇他，但我找不到反驳.

I can't find a counter-argument. I would never write code like that, but he's stubborn and says this is completely ok. If I was his boss, I would fire him for being a stubborn idiot, but I can't find a counter argument.

另一个例子:

int *number() {
    int n = 5;
    return &n;
}

int main() {
    int *a = number();
    int b = 9;
    int c = *a * b;
    printf("%d
", c);
}

在我得到一些好的答案后，我会把这个链接发给他，所以他至少学到了一些东西.

I will send him this link after I get some good answers, so he at least learns something.

推荐答案

你会遇到一个问题，当你在 name() 和 printf() 之间调用另一个函数时，它本身使用堆栈

you will get a problem, when you call another function between name() and printf(), which itself uses the stack

char *fun(char *what) {
   char res[10];
   strncpy(res, what, 9);
   return res;
}

main() {
  char *r1 = fun("bla");
  char *r2 = fun("blubber");
  printf("'%s' is bla and '%s' is blubber", r1, r2);
}

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