奇怪的段错误，可能与realloc有关 [英] strange seg fault, likely with realloc

问题描述

char *dumpTB (TB tb){

    char* text = malloc(sizeof(char));

    int i = 0; // 
    int x = 0; //string index

    tNode* curr = tb->head;

    while(curr != NULL){

        while(curr->line[x] != '\n'){
            printf("%d", i);
            text[i] = curr->line[x];
            printf("%c\n", text[i]);

            text = realloc(text, i+1);

            i++;
            x++;
        }
        text[i] = '\n';
        printf("%c", text[i]);
        text = realloc(text, i+1); 
        i++;

        x = 0; 
        curr = curr->next; 
    }

    return text;
}

所以我设法使用打印输出字符串的前12个字母语句，但是由于某种原因，它在打印第12个字母 l后不久给我一个段错误，并且基于打印语句，它似乎发生在重新分配周围...有人可以告诉我我做错了什么吗？

So I manage to print out the first 12 letters of my string using the print statements but for some reason it gives me a seg fault shortly after printing the 12th letter 'l', and based on the print statements it seems to occur around the realloc...can anyone tell me what I did wrong?

int i = 1; // 
    int x = 0; //string index

    tNode* curr = tb->head;

    while(curr != NULL){

        while(curr->line[x] != '\n'){
            printf("%d", i-1);
            text[i-1] = curr->line[x];
            printf("%c\n", text[i-1]);

            text = realloc(text, i+1);
            i++;
            x++;
        }
        printf("%d\n", i-1);
        text[i-1] = '\n';
        printf("%c", text[i-1]);
        text = realloc(text, i+1); 
        i++;

        x = 0; 
        curr = curr->next; 
        //printf("%c\n", curr->line[0]);
    }

我试图修复索引错误，这是一个看起来很长的sysmalloc断言东西，会中止

I tried fixed the index errors, a really long looking sysmalloc assertion thing which aborts the program.

推荐答案

您可能想要 getline（3），因此使用如果有的话。如 AnT的答案所述，您有未定义的行为（UB），原因是缓冲区溢出。尽快解决。对UB非常害怕，并花更多的时间来了解它（这很棘手）。

You probably want getline(3), so use it if you have it. As explained by AnT's answer, you have undefined behavior (UB) because of a buffer overflow. Fix that as soon as possible. Be very scared of UB and take more time to read about it (it is tricky).

另外，请记住，两个 malloc（3 ）和 realloc（3）昂贵的通话（对于昂贵的一些适当概念；实际上，它们非常快-合理使用时通常在桌面上不到一微秒），并且它们可能会失败（通过提供 NULL ），您应该检查。

Also, remember that both malloc(3) and realloc(3) are somehow expensive calls (for some suitable notion of expensive; actually, they are quite fast - often less than a microsecond on a desktop for reasonable use), and they could fail (by giving NULL) and you should check that.

实际上，您最好减少使用 realloc 的频率。根据经验，您希望将使用的长度和分配的大小都保留在某个位置（例如，在其他局部变量中），并且可能使用一些几何级数（例如， newsize = 4 * oldsize / 3 + 10 ....），以避免太频繁地 realloc -s。为每个额外的字节执行 realloc 是很难的。

In practice, you'll better use realloc less often. As a rule of thumb, you want to keep both the used length and the allocated size somewhere (e.g. in additional local variables), and you might use some geometrical progression (e.g. newsize = 4*oldsize/3 + 10....) to avoid too frequent realloc-s. Doing a realloc for each additional byte is ugly.

使用所有警告和调试信息来编译代码，例如 gcc -Wall -Wextra -g 和 GCC 。改进代码以获得任何警告。 使用调试器 gdb 和< a href = http://valgrind.org/ rel = nofollow noreferrer> valgrind 来狩猎内存泄漏和其他麻烦。

Compile your code with all warnings and debug info, e.g. gcc -Wall -Wextra -g with GCC. Improve the code to get no warnings. Use the debugger gdb and valgrind to hunt memory leaks and other trouble.

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