Linux getgrent() 导致“分段错误”

Question

我正在尝试打印所有系统组（Ubuntu 20.04）：

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <grp.h>

int main(int argc, char *argv[])
{
   printf("Here are all of this system's groups:\n\n");

   struct group* grp;
   while ((grp = getgrent()) != NULL)
      puts(grp->gr_name);

   endgrent();
   
   exit(EXIT_SUCCESS);
}

我用sudo 运行程序，我得到：

$ sudo ./program
Here are all of this system's groups:

Segmentation fault

使用struct spwd 时会发生同样的错误。

更新

我用include 行更新了源代码，并省略了lib/*.c 部分。当我编译这段代码时：

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: [...]
Thread model: posix
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)

$ gcc -std=c17 main.c -o program
main.c: In function ‘main’:
main.c:11:18: warning: implicit declaration of function ‘getgrent’ [-Wimplicit-function-declaration]
   11 |    while ((grp = getgrent()) != NULL)
      |                  ^~~~~~~~
main.c:11:16: warning: assignment to ‘struct group *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
   11 |    while ((grp = getgrent()) != NULL)
      |                ^
main.c:14:4: warning: implicit declaration of function ‘endgrent’ [-Wimplicit-function-declaration]
   14 |    endgrent();
      |    ^~~~~~~~

当我运行它时：

$ ./program 
Here are all of this system's groups:

Segmentation fault (core dumped)

$ sudo ./program 
Here are all of this system's groups:

Segmentation fault

现在，当我运行 VS Code 调试器时，它可以正常工作。 VS Code 根据this article配置。

这是我的launch.json：

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "gcc-9 - Build and debug active file",
            "type": "cppdbg",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${fileDirname}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                }
            ],
            "preLaunchTask": "C/C++: gcc-9 build active file",
            "miDebuggerPath": "/usr/bin/gdb"
        }
    ]
}

Answer 1

添加正确的标题：

---

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <grp.h>

int main(int argc, char *argv[])
{
   printf("Here are all of this system's groups:\n\n");

   struct group* grp;
   while ((grp = getgrent()) != NULL)
      puts(grp->gr_name);

   endgrent();

   exit(EXIT_SUCCESS);
}

---

更新：-std=c17 很奇怪，它没有包含 <grp.h> 。你可能需要std=gnu17，其中包括一些 gnu+posix 的东西。