在 C89 中，我似乎无法从现有的字符数组中创建一个字符数组

Question

所以我的代码在 buffer[i] = envp[i] 处崩溃了。

我想创建一个 char** 环境变量缓冲区，并将它们设为小写（尚未添加 putc(tolower()) 循环）。但是当我只是尝试使 buffer[i] = envp[i] 时，编译器 returns 我这个错误：

error: assignment makes integer from pointer without a cast [-Wint-conversion] buffer[i] = envp[i]; ^

warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [-Wformat=] printf("%s\n", buffer[i]); ~^ ~~~~~~~~~ %d

int main(int argc, char *argv[], char * envp[])
{
    int i = 0;

    char *buffer = NULL;

    while(envp[i])
    {
        i++;
    }

    buffer = (char *)malloc(i * 8);


    for (i = 0; envp[i] != 0 ; i++)
    {
        buffer[i] = envp[i];
        printf("%s\n", envp[i]);
        printf("%s\n", buffer[i]);
    }

    return 0;

}

请帮忙，我一直在这里伤脑筋:(。非常感谢！！！

Answer 1

char * envp[] 是指向字符的指针数组，而不是字符数组。指针（envp[i]）是一个整数。当您尝试将其分配给 buffer[i]（这是一个字符）时，您会收到警告。

Answer 2

buffer 不是保存字符串数组的正确类型。应该定义为：

char **buffer;

此外，您应该malloc如下：

buffer = malloc(i * sizeof(*buffer));

明确使用 sizeof(*buffer) 而不是幻数 8，因为不能保证指针是 8 个字节。这也优于 sizeof(char *)，因为它不依赖于 buffer 的类型此外，don't cast the return value of malloc.

由于 env 由 NULL 指针终止，因此您需要对 buffer 执行相同的操作。您还应该使用 strdup 复制字符串，而不仅仅是复制指针，这样您就可以处理单独的副本：

char **buffer = malloc((i+1) * sizeof(*buffer));

for (i = 0; envp[i] != 0 ; i++)
{
    buffer[i] = strdup(envp[i]);
    printf("%s\n", envp[i]);
    printf("%s\n", buffer[i]);
}
buffer[i] = NULL;

Answer 3

感谢大家的反馈，在这里评论后我能够修复我的功能。为帮助干杯！！！

char **lower_env(int argc, char *argv[], char * envp[])
{
    int i = 0;
    int k = 0;
    int length = 0; /*Going to dictate lengths later on*/
/*creating the double buffer*/
char **buffer;

/* Finding the amount of elements in the environment array*/
while (envp[i])
{
    i++;
}

/* Allocate the memory for the Buffer to hold that amount of elements*/
buffer = calloc(i+1, (sizeof(char*)));


for (i = 0; envp[i] ; i++)
{

    length = strlen(envp[i]); /*Finding the length of each array pointed
                                at by the original environment array*/

    buffer[i] = calloc(length+1 , sizeof(char)); /*Allocating that memory space
                                                        within our buffer array*/


    /*copying over the arrays in lowercase pointed at by the env array to a new memory location
        pointed at by our new buffer array*/
    for (k = 0; k != length; k++)
    {
        buffer[i][k] = tolower (envp[i][k]);
    }
}

return buffer;
}

在 C89 中，我似乎无法从现有的字符数组中创建一个字符数组

In C89, I can't seem to make a character array from an existing one

c

c89