程序在重新分配內存時導致內存損壞

我有一個2D數組的程序。首先，我分配陣列是這樣的：程序在重新分配內存時導致內存損壞

char **crossword; 
crossword = (char **) malloc(n* sizeof(*crossword)); 
for (i = 0; i < n; i++) 
    crossword[i] = (char *)malloc(n);

其中n = 50。

然後我有功能，即從stdin讀取字符串。問題是，我不知道這些字符串會有多少或多長時間。

void read(char **p,int *n) 
{ 
char tmp = 0,prevtmp = 0; 
int i = 0, j = 0,x; 

while (1) 
{ 
    prevtmp = tmp; 
    tmp = getchar(); 
    if ((tmp == '\n' && prevtmp == '\n') || feof (stdin)) 
    { 
     *n = i; 
     break; 
    } 
    if (tmp == '\n') 
    { 
     p[i][j] = '\0'; 
     i++; 
     if (i == *n) 
     { 
      p = (char **) realloc(p, 2*i); // if there is more strings than space for them, allocate more memory. 
      for (x = i; x < 2*i; x++) 
       p[x] = (char *) malloc (*n); 

      *n *= 2; 
     } 
     j = 0; 
     continue; 
    } 
    p[i][j] = tmp; 
    j++; 
    if (j == *n) 
     p[i] = (char *)realloc(p[i], 2*j); //same as above 
} 
}

函數被調用是這樣的：

read(crossword,&n);

此功能工作正常，在沒有必要的realloc（有小於50串，每一個小於50個字符）。但對於大的投入，這將失敗，並

*** glibc detected *** ./a.out: malloc(): memory corruption (fast): 0x00000000014282f0 *** error.

我想我的問題是，我的realloc更多的內存部分，這裏是從Valgrind的輸出：

==8885== Invalid write of size 1 
==8885== at 0x40084C: read (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out) 
==8885== by 0x40177F: main (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out) 
==8885== Address 0x51f2b88 is not stack'd, malloc'd or (recently) free'd 
==8885== 
==8885== Invalid write of size 8 
==8885== at 0x4008A6: read (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out) 
==8885== by 0x40177F: main (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out) 
==8885== Address 0x51f4f00 is not stack'd, malloc'd or (recently) free'd 

valgrind: m_mallocfree.c:266 (mk_plain_bszB): Assertion 'bszB != 0' failed. 
valgrind: This is probably caused by your program erroneously writing past the 
end of a heap block and corrupting heap metadata. If you fix any 
invalid writes reported by Memcheck, this assertion failure will 
probably go away. Please try that before reporting this as a bug. 

==8885== at 0x3804C6CF: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x3804C812: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x38000883: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x380574EA: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x38057E03: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x380212DC: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x3802146A: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x3808F656: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 
==8885== by 0x3809E68C: ??? (in /usr/lib/valgrind/memcheck-amd64-linux) 

sched status: 
    running_tid=1 

Thread 1: status = VgTs_Runnable 
==8885== at 0x4C2B3F8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) 
==8885== by 0x4008A5: read (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out) 
==8885== by 0x40177F: main (in /home/xerw/Dropbox/CVUT/PROGTEST/du6/a.out)

我一直在嘗試與指針很短的時間，所以我不知道什麼是錯的。我一直試圖解決這個問題幾個小時，但我沒有提出任何問題。

我在做什麼錯？

來源

2012-11-24 isklenar

什麼是填字遊戲的類型？ – piokuc

char **填字遊戲，編輯我的帖子。 – isklenar

你在你的代碼中執行'p =（char **）realloc（p，2 * i）;'。 'p'指向填字遊戲嗎？如果是這樣，你已經分配了縱橫字符，大小爲'n * sizeof（*縱橫字謎）'。那麼'2 * i'是否正確？順便說一下，調用realloc並將其結果指定給您直接重新分配的指針是不好的 - 如果realloc（）失敗，它會泄漏內存，導致原始指針現在丟失。 –

的問題似乎是以下行：

p = (char **) realloc(p, 2*i);

我想這應該是：

p = (char **) realloc(p, (2*i)*sizeof(char*));

即要增加數組來保存2*i元素，所以你需要分配2*i乘以char*的大小。

來源

2012-11-24 20:58:19 Raam

謝謝，解決了，但我的程序仍然崩潰，這次有一個不同的錯誤。我現在正在通過電話發帖，我不記得確切的錯誤，明天早上將會查看。 – isklenar

程序在重新分配內存時導致內存損壞

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