realpath 函数的转换问题（C 编程）

发布于 2024-08-07 21:49:57 字数 565 浏览 1 评论 0原文

当我编译以下代码时：

#define _POSIX_C_SOURCE 200112L
#define _ISOC99_SOURCE
#define __EXTENSIONS__

#include <stdio.h>
#include <limits.h>
#include <stdlib.h>    

int
main(int argc, char *argv[])
{
    char *symlinkpath = argv[1];
    char actualpath [PATH_MAX];
    char *ptr;
    ptr = realpath(symlinkpath, actualpath);
    printf("%s\n", ptr);
}

我在包含对 realpath 函数的调用的行上收到一条警告，内容为：

warning: assignment makes pointer from integer without a cast

有人知道发生了什么吗？我运行的是 Ubuntu Linux 9.04

原文

When I compile the following code:

#define _POSIX_C_SOURCE 200112L
#define _ISOC99_SOURCE
#define __EXTENSIONS__

#include <stdio.h>
#include <limits.h>
#include <stdlib.h>    

int
main(int argc, char *argv[])
{
    char *symlinkpath = argv[1];
    char actualpath [PATH_MAX];
    char *ptr;
    ptr = realpath(symlinkpath, actualpath);
    printf("%s\n", ptr);
}

I get a warning on the line that contains the call to the realpath function, saying:

warning: assignment makes pointer from integer without a cast

Anybody know what's up? I'm running Ubuntu Linux 9.04

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み零 2024-08-14 21:49:57

这很简单。 Glibc 将 realpath() 视为 GNU 扩展，而不是 POSIX。因此，添加以下行：

#define _GNU_SOURCE

... 在包含 stdlib.h 之前，以便它具有原型并已知返回 char *。否则，gcc 将假定它返回默认类型 int。除非定义了 _GNU_SOURCE ，否则看不到 stdlib.h 中的原型。

以下内容符合要求，没有通过 -Wall 发出警告：

#include <stdio.h>
#include <limits.h>

#define _GNU_SOURCE
#include <stdlib.h>

int
main(int argc, char *argv[])
{
    char *symlinkpath = argv[1];
    char actualpath [PATH_MAX];
    char *ptr;
    ptr = realpath(symlinkpath, actualpath);
    printf("%s\n", ptr);

    return 0;
}

您将看到其他流行扩展（例如 asprintf()）的类似行为。值得一看 /usr/include/ 以准确了解该宏打开的程度以及它发生的变化。

This is very simple. Glibc treats realpath() as a GNU extension, not POSIX. So, add this line:

#define _GNU_SOURCE

... prior to including stdlib.h so that it is prototyped and known to to return char *. Otherwise, gcc is going to assume it returns the default type of int. The prototype in stdlib.h is not seen unless _GNU_SOURCE is defined.

The following complies fine without warnings with -Wall passed:

#include <stdio.h>
#include <limits.h>

#define _GNU_SOURCE
#include <stdlib.h>

int
main(int argc, char *argv[])
{
    char *symlinkpath = argv[1];
    char actualpath [PATH_MAX];
    char *ptr;
    ptr = realpath(symlinkpath, actualpath);
    printf("%s\n", ptr);

    return 0;
}

You will see similar behavior with other popular extensions such as asprintf(). Its worth a look at /usr/include/ to see exactly how much that macro turns on and what it changes.

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