C語言擴展動態內存報錯：realloc(): invalid next size: 0x0000000002365010 ***

　　晚上被這個內存擴展崩潰的問題折騰的有點崩潰，當答案揭曉的那一刻，恍然大悟，原來如此簡單。

　　練習題目：輸入一個字符串，根據字母進行排序，說白了就是一個簡單的冒泡

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

#define BUF_LEN 100
#define COUNT 5

int main(void)
{
        char buf[BUF_LEN];
        size_t str_count = 0;
        size_t capacity = COUNT;
        char **pS = calloc(capacity, sizeof(char*));
        char **psTemp = NULL;
        char *pTemp = NULL;
        size_t str_len = 0;
        bool sorted = false;

        printf("Enter strings to be sorted, one per line. Press Enter to end:\n");

        char *ptr = NULL;

        while(true)
        {
                ptr = fgets(buf, BUF_LEN, stdin);
                if(!ptr)
                {
                        printf("Error reading string.\n");
                        free(pS);
                        pS = NULL;
                        return 1;
                }

                if(*ptr == '\n')
                        break;

                if(str_count == capacity)
                {
                        capacity += capacity/4;

                        if(!(psTemp = realloc(pS, capacity)))
                                return 1;
                        pS = psTemp;
                }

                str_len = strlen(buf) + 1;

                if(!(pS[str_count] = malloc(str_len)))
                        return 2;
                strcpy(pS[str_count++], buf);
        }

        while(!sorted)
        {
                sorted = true;
                size_t i = 0;
                for(; i < str_count - 1; i++)
                {
                        if(strcmp(pS[i], pS[i+1]) > 0)
                        {
                                sorted = false;
                                pTemp = pS[i];
                                pS[i] = pS[i+1];
                                pS[i + 1] = pTemp;
                        }

                }
        }

        printf("Your input sorted in ascending sequence is:\n\n");
        size_t i = 0;
        for(; i < str_count; i++)
        {
                printf("%s", pS[i]);
                free(pS[i]);
                pS[i] = NULL;
        }
        free(pS);
        pS = NULL;

        return 0;
}

                                     

　　上面標黃處，首先是通過calloc進行內存分配，初始是capacity的長度是5，接着判斷當輸入的字符串個數等於5了，那么就動態的擴展內存，繼續按25%的速度增長。就是在擴展這里，一直報錯：

*** Error in `./program714.out': realloc(): invalid next size: 0x0000000002365010 ***
======= Backtrace: =========
/lib64/libc.so.6(+0x7f5d4)[0x7f476bff35d4]
/lib64/libc.so.6(+0x83bd8)[0x7f476bff7bd8]
/lib64/libc.so.6(realloc+0x1d2)[0x7f476bff9832]
./program714.out[0x4008ea]
/lib64/libc.so.6(__libc_start_main+0xf5)[0x7f476bf963d5]
./program714.out[0x400729]
======= Memory map: ========
00400000-00401000 r-xp 00000000 fd:01 1321539                            /home/wlf/practice/program714.out
00600000-00601000 r--p 00000000 fd:01 1321539                            /home/wlf/practice/program714.out
00601000-00602000 rw-p 00001000 fd:01 1321539                            /home/wlf/practice/program714.out
02365000-02386000 rw-p 00000000 00:00 0                                  [heap]
7f4764000000-7f4764021000 rw-p 00000000 00:00 0 
7f4764021000-7f4768000000 ---p 00000000 00:00 0 
7f476bd5e000-7f476bd73000 r-xp 00000000 fd:01 655380                     /usr/lib64/libgcc_s-4.8.5-20150702.so.1
7f476bd73000-7f476bf72000 ---p 00015000 fd:01 655380                     /usr/lib64/libgcc_s-4.8.5-20150702.so.1
7f476bf72000-7f476bf73000 r--p 00014000 fd:01 655380                     /usr/lib64/libgcc_s-4.8.5-20150702.so.1
7f476bf73000-7f476bf74000 rw-p 00015000 fd:01 655380                     /usr/lib64/libgcc_s-4.8.5-20150702.so.1
7f476bf74000-7f476c136000 r-xp 00000000 fd:01 658657                     /usr/lib64/libc-2.17.so
7f476c136000-7f476c336000 ---p 001c2000 fd:01 658657                     /usr/lib64/libc-2.17.so
7f476c336000-7f476c33a000 r--p 001c2000 fd:01 658657                     /usr/lib64/libc-2.17.so
7f476c33a000-7f476c33c000 rw-p 001c6000 fd:01 658657                     /usr/lib64/libc-2.17.so
7f476c33c000-7f476c341000 rw-p 00000000 00:00 0 
7f476c341000-7f476c363000 r-xp 00000000 fd:01 658372                     /usr/lib64/ld-2.17.so
7f476c557000-7f476c55a000 rw-p 00000000 00:00 0 
7f476c55e000-7f476c562000 rw-p 00000000 00:00 0 
7f476c562000-7f476c563000 r--p 00021000 fd:01 658372                     /usr/lib64/ld-2.17.so
7f476c563000-7f476c564000 rw-p 00022000 fd:01 658372                     /usr/lib64/ld-2.17.so
7f476c564000-7f476c565000 rw-p 00000000 00:00 0 
7ffde3137000-7ffde3158000 rw-p 00000000 00:00 0                          [stack]
7ffde31c5000-7ffde31c7000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
Aborted

　　代碼看來看去發現沒毛病，唯一能懷疑的地方就是內存擴展的那一行，經過幾番折騰，發現只要一到需要增長調用realloc就報錯，最后回去看calloc，只能一拍大腿罵娘了，字節計算的類型不對啊，一個是按char*（相當於二維數組pS[][]中的子數組pS[]）來計算字節，一個是按字符（char）來計算字節，得到的內存大小必然不同啊。把realloc的第二個參數加上這個就解決了：　　

if(!(psTemp = realloc(pS, capacity*sizeof(char*))))

　　編碼需謹慎，差之毫厘，謬之千里，一點小小的bug都能讓程序崩潰。