无法将内存分配给指针的指针

Question

我的问题是无法将内存分配给 (char*) 指针，我似乎不明白为什么。我回顾了其他类似的问题，但我似乎无法掌握答案。我正在尝试 return 一个字符串列表，但我知道在 C 中我不能 return char**，但我可以通过 char** 参数做到这一点。我的尝试在下面的代码片段中。

在a.c

void list(char** fileList) {
    int fileIndex = 0;
    fileList = (char**)malloc(DIRECTORY_SIZE * sizeof(char*));
    while ((dir = readdir(currentDirectory)) != NULL)
    {
       fileList[fileIndex] = (char*)malloc(FILENAME_LENGTH * sizeof(char)); //It fails here
       fileList[fileIndex] = strncpy(fileList[fileIndex], dir->d_name, FILENAME_LENGTH);
       fileIndex++;
       printf("%s\n", fileList[fileIndex]);
    }
}

在main.c

int main() {
    char** fileList;
    list(fileList);
    for(int i = 0; i < 10; i++) {
        printf("%s\n", fileList[i]);
    }
}

我已经看过这些问题了：

Assigning memory to double pointer?
Assigning memory to double pointer?

Answer 1

发生的事情是内存指针 fileList 被复制到列表函数，当列表函数随后更改指针时，但初始指针不会改变。

要解决此问题，您可以给它一个指向指针的指针以更改实际指针值，如下所示：

void list(char*** fileList) {
    int fileIndex = 0;
    *fileList = (char**)malloc(DIRECTORY_SIZE * sizeof(char*));
    while ((dir = readdir(currentDirectory)) != NULL)
    {
       *fileList[fileIndex] = (char*)malloc(FILENAME_LENGTH * sizeof(char)); //It fails here
       *fileList[fileIndex] = strncpy(fileList[fileIndex], dir->d_name, FILENAME_LENGTH);
       fileIndex++;
       printf("%s\n", fileList[fileIndex]);
    }
}

int main() {
    char** fileList;
    list(&fileList);
    for(int i = 0; i < 10; i++) {
        printf("%s\n", fileList[i]);
    }
}

但我个人觉得这样有点笨拙，所以最好这样做:

char** list(void) {
    char** fileList;
    int fileIndex = 0;
    fileList = (char**)malloc(DIRECTORY_SIZE * sizeof(char*));
    while ((dir = readdir(currentDirectory)) != NULL)
    {
       fileList[fileIndex] = (char*)malloc(FILENAME_LENGTH * sizeof(char)); //It fails here
       fileList[fileIndex] = strncpy(fileList[fileIndex], dir->d_name, FILENAME_LENGTH);
       fileIndex++;
       printf("%s\n", fileList[fileIndex]);
    }
    return filelist;
}

int main() {
    char** fileList = list();
    for(int i = 0; i < 10; i++) {
        printf("%s\n", fileList[i]);
    }
}

无法将内存分配给指针的指针

Failing to assign memory to a pointer of a pointer

c

pointers

memory-management