使用realloc动态扩展数组

Question

我已经编写了以下代码来清楚地了解malloc和realloc.我使用malloc初始化指针然后使用realloc,我增加了数组的大小.但是当我运行代码时,我得到以下错误.

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

int main()
{
    char *p;
    p = malloc(10);
    p = " this is it";
    printf("\n%s", p);
    p = realloc(p, 14);
    p[11] = 'A';
    p[12] = 'B';
    p[13] = 'C';
    printf("\n %s", p) ;
    return 0;
}

输出:

ajay@ajay-K54L:~$ gcc te.c 
ajay@ajay-K54L:~$ ./a.out

*** glibc detected *** ./a.out: realloc(): invalid pointer: 0x000000000040071c ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7e626)[0x7fb111e88626]
/lib/x86_64-linux-gnu/libc.so.6(realloc+0x2de)[0x7fb111e8d3ee]
./a.out[0x4005dc]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7fb111e2b76d]
./a.out[0x4004d9]
======= Memory map: ========
00400000-00401000 r-xp 00000000 08:03 3027043                            /home/ajay/a.out
00600000-00601000 r--p 00000000 08:03 3027043                            /home/ajay/a.out
00601000-00602000 rw-p 00001000 08:03 3027043                            /home/ajay/a.out
00e76000-00e97000 rw-p 00000000 00:00 0                                  [heap]
7fb111bf4000-7fb111c09000 r-xp 00000000 08:03 2100801                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fb111c09000-7fb111e08000 ---p 00015000 08:03 2100801                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fb111e08000-7fb111e09000 r--p 00014000 08:03 2100801                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fb111e09000-7fb111e0a000 rw-p 00015000 08:03 2100801                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fb111e0a000-7fb111fbd000 r-xp 00000000 08:03 2100780                    /lib/x86_64-linux-gnu/libc-2.15.so
7fb111fbd000-7fb1121bc000 ---p 001b3000 08:03 2100780                    /lib/x86_64-linux-gnu/libc-2.15.so
7fb1121bc000-7fb1121c0000 r--p 001b2000 08:03 2100780                    /lib/x86_64-linux-gnu/libc-2.15.so
7fb1121c0000-7fb1121c2000 rw-p 001b6000 08:03 2100780                    /lib/x86_64-linux-gnu/libc-2.15.so
7fb1121c2000-7fb1121c7000 rw-p 00000000 00:00 0 
7fb1121c7000-7fb1121e9000 r-xp 00000000 08:03 2100760                    /lib/x86_64-linux-gnu/ld-2.15.so
7fb1123d2000-7fb1123d5000 rw-p 00000000 00:00 0 
7fb1123e5000-7fb1123e9000 rw-p 00000000 00:00 0 
7fb1123e9000-7fb1123ea000 r--p 00022000 08:03 2100760                    /lib/x86_64-linux-gnu/ld-2.15.so
7fb1123ea000-7fb1123ec000 rw-p 00023000 08:03 2100760                    /lib/x86_64-linux-gnu/ld-2.15.so
7ffff08d4000-7ffff08f5000 rw-p 00000000 00:00 0                          [stack]
7ffff09ff000-7ffff0a00000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
 this is itAborted (core dumped)

我在内存分配上做错了什么？谢谢.

Answer 1

这个:

p = " this is it"; /* Does not copy, use strcpy(). */

指定字符串文字p的地址,从之前返回的地址改变它malloc().传递给的指针realloc()必须是:

...之前由malloc(),calloc()或realloc()分配但尚未使用free()释放,否则,结果是未定义的.

将分配更改strcpy()为例如更正:

p = malloc(12); /* Increased size. */
if (p)
{
    strcpy(p, " this is it");
    char* tmp = realloc(p, 14);  /* Store result in temp to avoid potential */
    if (!tmp)                    /* in the event that realloc() fails. */
    {
        free(p);
        return -1;
    }
    p = tmp;
    /* snip ... */

    free(p); /* When 'p' is no longer required. */
}