函数C内的realloc [英] C realloc inside a function

问题描述

下面是我的code：

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>

void mp3files(char** result, int* count, const char* path) {
    struct dirent *entry;
    DIR *dp;

    dp = opendir(path);
    if (dp == NULL) {
        printf("Error, directory or file \"%s\" not found.\n", path);
        return;
    }

    while ((entry = readdir(dp))) {
        if ((result = (char**) realloc(result, sizeof (char*) * ((*count) + 1))) == NULL) {
            printf("error");
                return;
        }

        result[*count] = entry->d_name;
        (*count)++;
    }

    closedir(dp);
}

int main() {

    int* integer = malloc(sizeof (int));
    *integer = 0;

    char** mp3FilesResult = malloc(sizeof (char*));
        mp3files(mp3FilesResult, integer, ".");

    for (int i = 0; i < *integer; i++) {
        printf("ok, count: %d \n", *integer);
        printf("%s\n", mp3FilesResult[i]);
    }

    return (EXIT_SUCCESS);
}

这给了我segmetation故障。然而，当我把这个循环：

It gives me segmetation fault. However, when I put this loop:

for (int i = 0; i < *integer; i++) {
    printf("ok, count: %d \n", *integer);
    printf("%s\n", mp3FilesResult[i]);
}

在mp3files函数的最后，它的工作原理。而当我改变mp3files第三parametr的功能。到包含小于4的文件或目录的目录，它的伟大工程。换句话说，当小于4个字符串变量mp3FilesResult点，它不会失败，Segmetation故障。

in the end of mp3files function, it works. And when I change the third parametr of mp3files function from "." to a directory which contains less then 4 files or directories, it works great. In other words, when variable mp3FilesResult points at less then 4 strings, it doesn't fail with Segmetation fault.

为什么它继续做下去？

Why does it keep doing it ?

在此先感谢和抱歉，我的英语水平。

Thanks in advance and sorry for my english.

推荐答案

您传递一个的char ** ，一个指向字符指针，这是重新presenting指针弦，这是重新presenting字符串数组。如果你想重新分配数组，你必须通过引用传递它（一个指针传递给它），所以你需要一个的指针的字符串数组，或的char ** * ：

You pass in a char **, a pointer to a pointer to char, which is representing pointer to "string" which is representing "array of string". If you want to reallocate that array you must pass it by reference (pass a pointer to it) so you need a "pointer to array of string", or a char ***:

... myfunc(char ***result, ...)
{
    *result = realloc(*result, ...); // writing *result changes caller's pointer
}


...
char **data = ...;
myfunc(&data, ...);

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