Linux getgrent() 导致“分段错误”

Question

I'm trying to print all of system's groups (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);
}

I run the program with sudo and I get:

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

Segmentation fault

Same error happens when working with struct spwd .

Update

I updated the source with the include lines and I left out the lib/*.c part. When I compile this exact piece of code:

$ 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();
      |    ^~~~~~~~

And When I run it:

$ ./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

Now when I run VS Code debugger it works correctly. VS Code is configured according to this article .

Here's my 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

Add the correct headers:

---

#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);
}

---

Update: -std=c17 is strange, it fails to include <grp.h> . You probably need std=gnu17 , which includes some gnu+posix stuff.