Realloc：拆分行时下一个大小无效答案

【问题标题】：Realoc: invalid next size while splitting a lineRealloc：拆分行时下一个大小无效
【发布时间】：2014-11-23 19:38:11
【问题描述】：

我的代码将 char* 行拆分为 char*** cmds，首先按字符 '|'然后是空格、\n 等。示例 I/O：

我：line = "ls -l / | unique | sort"

O：cmds = {{"ls", "-l", "/", NULL}, {unique, NULL}, {sort, NULL}, NULL}

现在，每当到达*cmds = realloc(*cmds, nlines+1); 行超过 1 个字时，它就会产生错误

*** Error in ./a.out': realloc(): invalid next size: 0x000000000114c010 *** 或

a.out: malloc.c:2372: sysmalloc: Assertion (old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 *(sizeof(size_t))) - 1)) & ~((2 *(sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long) old_end & pagemask) == 0)' failed.

任何帮助将不胜感激，我已经花费了数小时的时间......

void parse(char *line, char *** cmds)
{
printf("got line %s\n", line);
    size_t nlines = 0;
    *cmds =  NULL;

    while (*line != '\0') {
    nlines++;

        while (*line == ' ' || *line == '\t' || *line == '\n')
            *line++ = '\0'; 

        *cmds = realloc(*cmds, nlines+1);
        (*cmds)[nlines-1] = line; 
        (*cmds)[nlines] = NULL;    

        while (*line != '\0' && *line != ' ' && *line != '\t' && *line != '\n')
            line++;
    }
    **cmds = '\0';  
}

void parsePipe(char *line, char ***cmds)
{
    char *cmd = strtok(line, "|");
    int linesFound = 0;

    while (cmd != NULL) 
    {
       printf("Printing word -> %s\n", cmd);
       linesFound++; 
       parse(cmd, cmds++);

       cmd = strtok(NULL, "|");
    }

    printf("This string contains %d lines separated with |\n",linesFound);
}

void  main(void)
{
    char  line[1024];          
    char  **cmds[64] = {0};

    while (1) {    
        printf("lsh -> ");   
        gets(line);     
        printf("\n");
        parsePipe(line, cmds);  
    }
}

【问题讨论】：

你在这里只分配 nlines+1 个字节：*cmds = realloc(*cmds, nlines+1);。您需要为 nlines+1 指针留出空间。
另外，**cmds = '\0。 **cmds 是指向字符的指针，而不是字符。 c2.com/cgi/wiki?ThreeStarProgrammer
你能告诉我如何解决这个问题吗？我不知道该怎么做，目前也没有时间学习：/
使用模式p = realloc(p, N * sizeof *p)。这将为 p 指向的任何 N 项目分配空间。
如果你画出所有字符缓冲区和指针在内存中的位置，你可能会发现更容易理解你的代码

标签： c pointers segmentation-fault realloc

【解决方案1】：

要修复的样本

void parse(char *line, char *** cmds){
    char *cp, *token;
    size_t nlines = 0;
    *cmds =  NULL;

    token = strtok_r(line, " \t\n", &cp);
    while (token) {
        nlines++;
        *cmds = realloc(*cmds, sizeof(char*)*(nlines+1));
        (*cmds)[nlines-1] = token;
        (*cmds)[nlines] = NULL;
        token = strtok_r(NULL, " \t\n", &cp);
    }
}

void parsePipe(char *line, char ***cmds){
    char *cp;
    char *cmd = strtok_r(line, "|", &cp);
    int i=0, linesFound = 0;

    while (cmd != NULL){
        //printf("Printing word -> %s\n", cmd);
        linesFound++; 
        parse(cmd, cmds++);
        cmd = strtok_r(NULL, "|", &cp);
    }
    //printf("This string contains %d lines separated with |\n",linesFound);
    *cmds = NULL;
}

int  main(void){
    char  line[1024];
    char  **cmds[64] = {0};
    int i;

    while (1) { 
        printf("lsh -> ");
        scanf("%1023[^\n]%*c", line);
        if(*line == '.' && !line[1])
            break;
        parsePipe(line, cmds);
        //test print
        for(i=0; cmds[i]; ++i){
            int j=0;
            while(cmds[i][j]){
                printf("'%s' ", cmds[i][j++]);
            }
            printf("\n");
        }
    }
    //deallocation
    return 0;
}

【讨论】：