c - 指针所在的堆栈

Question

我在 APUE 中阅读了 make_tempory_file 演示，并对以下内容感到困惑:

char good_template[] = "/tmp/dirXXXXXX"; /* right way */
char *bad_template = "/tmp/dirXXXXXX"; /* wrong way*/

void make_temp(char *template);

int main()
{
    char  good_template[] = "/tmp/dirXXXXXX"; /* right way */
    char  *bad_template = "/tmp/dirXXXXXX"; /* wrong way*/

    printf("trying to create first temp file...\n");
    make_temp(good_template);
    printf("trying to create second temp file...\n");
    make_temp(bad_template);
    exit(0);
}

void make_temp(char *template)
{
    int fd;
    struct stat sbuf;

    if ((fd = mkstemp(template)) < 0)

        err_sys("can’t create temp file");
    printf("temp name = %s\n", template);
    close(fd);
    if (stat(template, &sbuf) < 0)
    {
        if (errno == ENOENT)

            printf("file doesn’t exist\n");
        else
            err_sys("stat failed");
    }
    else
    {
        printf("file exists\n");
        unlink(template);
    }
}

指令解释:

The difference in behavior comes from the way the two template strings are declared. For the first template, the name is allocated on the stack, because we use an array variable. For the second name, however, we use a pointer. In this case, only the memory for the pointer itself resides on the stack; the compiler arranges for the string to be stored in the read-only segment of the executable. When the mkstemp function tries to modify the string, a segmentation fault occurs.

我试图理解这个陈述，但坚持 stack

它指的是箭头所指的堆栈吗？

Answer 1

When the mkstemp function tries to modify the string, a segmentation fault occurs.

原因是因为字符串声明为char *bad_template = "/tmp/dirXXXXXX"; bad_template被分配给字符串文字。

在 C ，修改字符串文字是未定义的行为

引用 - C99 标准第 6.4.5-6 节

A character string literal is a sequence of zero or more multibyte characters enclosed in double-quotes, as in "xyz". A wide string literal is the same, except prefixed by the letter L.

If the program attempts to modify such an array, the behavior is undefined.