调用g_free()释放g_date_time_format()返回值触发无效指针错误原因

我通过当前系统时间生成日期字符串，按照GLib DateTime format文档说明，需要用g_free()释放g_date_time_format()的返回结果，但调用该函数时触发了free(): invalid pointer错误，请问这是什么原因？

代码示例 #

#include <glib.h>
#include <stdio.h>

int main(int argc, char *argv[]) 
{
    GDateTime *date_time = g_date_time_new_now_local();
    gchar *date_time_string = g_date_time_format(date_time, "%H:%M:%S");
    if (date_time_string == NULL) {
        g_print("it is null\n");
    } else {
        g_print("%s\n",date_time_string);
        g_free(date_time_string); /* abort occurs here */
    }
    g_free(date_time);
    return 0;
}

程序输出 #

12:16:16
free(): invalid pointer
Aborted (core dumped)

GDB调试信息 #

使用gdb ./a.out运行程序，终止后执行bt命令得到以下结果：

Starting program: logging/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
12:38:00
free(): invalid pointer

Program received signal SIGABRT, Aborted.
__pthread_kill_implementation (no_tid=0, signo=6, threadid=140737348770880) at ./nptl/pthread_kill.c:44
44  ./nptl/pthread_kill.c: No such file or directory.
(gdb) bt
#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737348770880) at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (signo=6, threadid=140737348770880) at ./nptl/pthread_kill.c:78
#2  __GI___pthread_kill (threadid=140737348770880, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#3  0x00007ffff7c82476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4  0x00007ffff7c687f3 in __GI_abort () at ./stdlib/abort.c:79
#5  0x00007ffff7cc9676 in __libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7ffff7e1bb77 "%s\n") at ../sysdeps/posix/libc_fatal.c:155
#6  0x00007ffff7ce0cfc in malloc_printerr (str=str@entry=0x7ffff7e19744 "free(): invalid pointer") at ./malloc/malloc.c:5664
#7  0x00007ffff7ce2a44 in _int_free (av=<optimized out>, p=<optimized out>, have_lock=0) at ./malloc/malloc.c:4439
#8  0x00007ffff7ce5453 in __GI___libc_free (mem=<optimized out>) at ./malloc/malloc.c:3391
#9  0x000055555555522f in main (argc=1, argv=0x7fffffffe028) at a.c:16

问题原因与修复 #

核心问题是释放GDateTime对象的方式错误：g_date_time_new_now_local()创建的GDateTime对象属于GLib的引用计数式对象，不能用g_free()直接释放，必须调用g_date_time_unref()来减少引用计数，当引用计数降为0时，对象才会被自动销毁。

你当前用g_free(date_time)直接释放GDateTime对象，会破坏GLib内部的内存管理结构——要么是g_date_time_format()返回的字符串和GDateTime对象的内存区域存在关联，要么是GDateTime被错误释放后堆内存状态被破坏，最终导致后续对date_time_string调用g_free()时触发指针校验错误。

修复后的代码如下：

#include <glib.h>
#include <stdio.h>

int main(int argc, char *argv[]) 
{
    GDateTime *date_time = g_date_time_new_now_local();
    gchar *date_time_string = g_date_time_format(date_time, "%H:%M:%S");
    if (date_time_string == NULL) {
        g_print("it is null\n");
    } else {
        g_print("%s\n",date_time_string);
        g_free(date_time_string);
    }
    g_date_time_unref(date_time); // 替换为正确的释放方式
    return 0;
}

另外需要确认编译时是否正确链接GLib库，编译命令应类似：

gcc -o a.out a.c `pkg-config --cflags --libs glib-2.0`

确保使用GLib提供的内存管理函数和库实现一致，避免因链接错误导致的内存管理不兼容问题。

内容的提问来源于stack exchange，提问作者9-Pin