分段故障处理字符串的列C [英] Segmentation fault with array of strings C

问题描述

我已经做了断​​线成空格分隔的标记，然后拷贝每个单独字符串转换成字符串数组的程序。

程序运行正常，直到它到达for循环，并在成功添加一个字符串到数组中，并打印出来，程序崩溃。我调试了一下，发现

  ARGS [I] =的malloc（（strlen的（comm_str）+ 1）* sizeof的（炭））;
 

收益段错误那么第二次执行循环。同时调用堆栈打印出以下内容：

  

地址：75F943F9，功能：strlen的（），文件：C：\\ WINDOWS \\ SysWow64资料\\ msvcrt.dll.`

我想正确的程序自己，但没有结果。我原先以为循环尝试访问外边界地区，但我想我已经正确malloc分配的一切。

 的#include＆LT;＆string.h中GT;
＃包括LT＆;＆stdlib.h中GT;
＃包括LT＆;＆stdio.h中GT;诠释主（）{    焦炭** ARGS = NULL;
    字符输入[] =CMDLINE -s -r 20 -t参数-p 20名;    INT NUM = 0;
    字符* comm_str = strtok的（输入，）; / *令牌命令行* /    而（comm_str！= NULL）{/ *计数的令牌数量* /
        NUM ++;
        的printf（％S％d个\\ N，comm_str，strlen的（comm_str））;
        comm_str =的strtok（NULL，）;
    }
    的printf（\\ n）;    ARGS =的malloc（NUM * sizeof的（字符*））; / *分配内存的第一个字符串项* /
    如果（！参数）{
        返回0;
    }    comm_str = strtok的（输入，）; / *开始从开始tokening * /
    的for（int i = 0; I＆LT;民;我++）{
        ARGS [I] =的malloc（（strlen的（comm_str）+ 1）* sizeof的（炭））; / *分配内存的字符串* /
        如果（！ARGS [I]）{
            对于（INT B = 0; B＆LT;我; b ++）{
                免费（参数[B]）;
            }
            免费（参数）;
            返回0;
        }
        的strcpy（参数[I]，comm_str）;
        的printf（％S \\ n，ARGS [I]）;
        comm_str =的strtok（NULL，）;
    }    的printf（％d个\\ N，NUM）;}
 

解决方案

strtok的是，如你所知，改变字符串。

计算的字的数量后，字符串将包含一个字。因此，接下来的 strtok的将返回NULL。

计算的参数的数目以非破坏性的方式，或者使字符串的副本。

I have made a program that breaks a string into tokens separated by space and then copies each separate string into an array of strings.

Program works fine until it reaches for-loop and after successfully adding the first string into the array and printing it, program crashes. I debugged it and found that

args[i] = malloc((strlen(comm_str) + 1) * sizeof(char));

returns SEGFAULT then performing loop for the second time. Also call stack prints out the following:

Address: 75F943F9, Function: strlen(), File: C:\Windows\syswow64\msvcrt.dll.`

I tried to correct program myself, but with no result. I thought at first that loop tries to access out of bound region, but I think I have malloc'd everything correctly.

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

int main(){

    char **args = NULL;
    char input[] = "cmdline -s 20 -r -t parameter -p 20 filename";

    int num = 0;
    char *comm_str = strtok(input, " ");                            /*Tokens command line*/

    while(comm_str != NULL){                                        /*Counts number of tokens*/
        num++;
        printf("%s %d\n", comm_str, strlen(comm_str));
        comm_str = strtok(NULL, " ");
    }
    printf("\n");

    args = malloc(num * sizeof(char*));                          /*Allocates memory for the first string entry*/
    if(!args){
        return 0;
    }

    comm_str = strtok(input, " ");                                  /*Starts tokening from beginning*/
    for(int i = 0; i < num; i++){
        args[i] = malloc((strlen(comm_str) + 1) * sizeof(char));    /*Allocates memory for strings*/
        if(!args[i]){
            for(int b = 0; b < i; b++){
                free(args[b]);
            }
            free(args);
            return 0;
        }
        strcpy(args[i], comm_str);
        printf("%s\n", args[i]);
        comm_str = strtok(NULL, " ");
    }

    printf("%d\n", num);

}

解决方案

strtok is, as you know, altering the string.

After calculating the number of words, the string will contain a single word. Hence the next strtok will return NULL.

Calculate the number of arguments in a non-destructive way, or make a copy of the string.

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