为什么我的函数返回的垃圾，当它应该返回一个char？ [英] Why is my function returning garbage when it should return a char?

问题描述

我是C ++的新手学习语言并玩耍。我写了一段代码，我不明白的行为。有人可以解释为什么下面的代码打印出随机垃圾，而不是列表中第一个字符串的第一个字符（即 a ）。

I'm a newbie in C++ learning the language and playing around. I wrote a piece of code which behavior I don't understand. Could someone explain why the code below prints out random junk and not the first character of the first string in the list (that is a).

#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <ctime>
#include <climits>
#include <stdio.h>


char* str2char(std::string str)
{
    char cset[str.size()+1]; // +1 for the null character
    for(int i = 0; i < str.size(); i++)
    {
        cset[i] = str[i];
    }
    cset[str.size()] = '\0';
    return cset;
}

int main (int argc, char * const argv[]) {



    std::vector< std::string > ladontakadet;
    ladontakadet.push_back("aabcbbca");
    ladontakadet.push_back("abcdabcd");
    ladontakadet.push_back("cbbdcdaa");
    ladontakadet.push_back("aadcbdca");
    ladontakadet.push_back("cccbaaab");
    ladontakadet.push_back("dabccbaa");
    ladontakadet.push_back("ccbdcbad");
    ladontakadet.push_back("bdcbccad");
    ladontakadet.push_back("ddcadccb");
    ladontakadet.push_back("baccddaa");

    std::string v = ladontakadet.at(0);
    char *r;
    r = str2char(v);
    std::cout << r[0] << std::endl;
    return 0;
}

为什么是我返回的垃圾，当我期望它输出 a ？

Why is my returning garbage, when I'm expecting it to output a?

Thnx任何帮助！

此代码的输出是随机的。它不总是打印相同的字符..：S

P.S. The output of this code is random. It doesn't always print the same character..:S

推荐答案

如果你的目的是通过std的内容： ：string到修改char *的内容的函数：

If your aim is to pass the content of a std::string to a function modifying the content of a char*:

#include <iostream>
#include <vector>

void f(char* s) {
    s[0] = 'H';
}

std::vector<char> to_vector(const std::string& s) {
    return std::vector<char>(s.c_str(), s.c_str() + s.size() + 1);
}

int main(void)
{
    std::string s = "_ello";
    std::vector<char> t = to_vector(s);
    f(t.data());
    std::cout <<  t.data() << std::endl;
}

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