C段错误

Question

我是编码新手，所以我知道我可能会搞砸一些事情。我想创建一个 (number_of_text_words)x(number_of_letters_of every_word) 维度的数组，其中我将逐个字符保存单词并在末尾添加 '\0' ，以便被识别为字符串。这是我的代码:

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


int main(int argc, char **argv)
{
    FILE *myinput;
    int i,k,sum,words_num,j;
    char **dict=NULL;
    char *num_words=NULL;
    myinput = fopen("bug.txt","r");
    if (myinput == NULL)
    {
        fprintf(stderr, "ERROR:\n");
        return;
    }
    fseek(myinput,0,SEEK_END);
    int size = ftell(myinput);
    fseek(myinput,0,SEEK_SET);
    char *data = malloc(size);
    if (data==NULL)
    return -1;
    fread(data,size,1,myinput);



    fclose(myinput);


    sum=0;
    for (i=0;i<=size-1;i++)
    if (data[i]=='\n')
    sum++;//count the words by the spaces


    /*for (i=0;i<=size-1;i++)
printf("%c\n",data[i]);*/

    /*printf("\n%d\n",sum);*/

    dict=malloc(sum);//for saving the words
    if (dict==NULL)
    return -1;
    num_words=malloc(sum);//for saving the number of letters of each word
    if (num_words==NULL)
    return -1;
    j=0;
    for (i=0;i<sum;i++){
        words_num=0;
        while ((data[j++]!='\n'))
        words_num++;//allocate the exact needed memory for each word



        dict[i]=malloc(words_num+1);//FOR THE FINAL '\0'
        if (dict[i]==NULL)
        return -1;
        num_words[i]=words_num;

    }

    k=0;
    for (i=0;i<sum;i++){
        for(j=0;j<num_words[i];j++){
            if ((data[k]=='\n') || (data[k]==EOF))
            k++;
            if (k<size)
            dict[i][j]=data[k++];
        }
        if (k<=size)
        dict[i][j+1]='\0';
    }



    for (i=0;i<sum;i++)
    free(dict[i]);

    free(dict);

    free(num_words);

    free(data);
    return 0;
}

但它无法编译，因为它显示了段错误。更具体地说，-g 编译显示了以下内容:

* Error in `./crossword': free(): invalid next size (fast): 0x0000000000fdf010 * ======= Backtrace: ========= /lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7f7b54dc87e5] /lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7f7b54dd137a] /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f7b54dd553c] ./crossword[0x400a97] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f7b54d71830] ./crossword[0x400699] ======= Memory map: ======== 00400000-00401000 r-xp 00000000 08:25 532064
/home/nikos/Desktop/ergasies/ergasia_4/crossword 00600000-00601000 r--p 00000000 08:25 532064
/home/nikos/Desktop/ergasies/ergasia_4/crossword 00601000-00602000 rw-p 00001000 08:25 532064
/home/nikos/Desktop/ergasies/ergasia_4/crossword 00fdf000-01000000 rw-p 00000000 00:00 0 [heap] 7f7b50000000-7f7b50021000 rw-p 00000000 00:00 0 7f7b50021000-7f7b54000000 ---p 00000000 00:00 0 7f7b54b3b000-7f7b54b51000 r-xp 00000000 08:25 529319
/lib/x86_64-linux-gnu/libgcc_s.so.1 7f7b54b51000-7f7b54d50000 ---p 00016000 08:25 529319
/lib/x86_64-linux-gnu/libgcc_s.so.1 7f7b54d50000-7f7b54d51000 rw-p 00015000 08:25 529319
/lib/x86_64-linux-gnu/libgcc_s.so.1 7f7b54d51000-7f7b54f11000 r-xp 00000000 08:25 542663
/lib/x86_64-linux-gnu/libc-2.23.so 7f7b54f11000-7f7b55111000 ---p 001c0000 08:25 542663
/lib/x86_64-linux-gnu/libc-2.23.so 7f7b55111000-7f7b55115000 r--p 001c0000 08:25 542663
/lib/x86_64-linux-gnu/libc-2.23.so 7f7b55115000-7f7b55117000 rw-p 001c4000 08:25 542663
/lib/x86_64-linux-gnu/libc-2.23.so 7f7b55117000-7f7b5511b000 rw-p 00000000 00:00 0 7f7b5511b000-7f7b55141000 r-xp 00000000 08:25 542656 /lib/x86_64-linux-gnu/ld-2.23.so 7f7b55323000-7f7b55326000 rw-p 00000000 00:00 0 7f7b5533f000-7f7b55340000 rw-p 00000000 00:00 0 7f7b55340000-7f7b55341000 r--p 00025000 08:25 542656
/lib/x86_64-linux-gnu/ld-2.23.so 7f7b55341000-7f7b55342000 rw-p 00026000 08:25 542656
/lib/x86_64-linux-gnu/ld-2.23.so 7f7b55342000-7f7b55343000 rw-p 00000000 00:00 0 7fff2dca9000-7fff2dcca000 rw-p 00000000 00:00 0
[stack] 7fff2dd02000-7fff2dd05000 r--p 00000000 00:00 0
[vvar] 7fff2dd05000-7fff2dd07000 r-xp 00000000 00:00 0
[vdso] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0
[vsyscall] Aborted (core dumped)

我还创建了一个数组来保存每个单词的大小。我没有双重释放任何指针，也找不到任何“数组外”的写法。任何人都可以指出我的代码中出现问题的地方吗？我真的很感激:)

Answer 1

您没有在这里分配足够的空间

dict=malloc(sum);

应该是

dict = malloc(sum * sizeof(*dict));

因为你需要sum大小为void *的元素，但最好写成sizeof(*dict)，因为这样代码与 dict 的类型无关，如果您更改它，则无需修复 malloc()。

这看起来也很可疑，

num_words=malloc(sum);

你怎么知道每个单词的字符数与文件中的行数一样多？