Question

字符串包含由空格分隔的三个部分。前两部分是字符串，第三部分是整数。

以下程序的输出令我感到惊讶。

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

void split(char *ch,char **part1,char **part2,int *num){
    int length=strlen(ch), *lc1,*lc2;
    int i=0,j=0;
    printf("value of length is %d\n",length);

    printf("this function recieved %s for splitting into pieces\n",ch);

    lc1=(char *)malloc(length*sizeof(char));
    lc2=(char *)malloc(length*sizeof(char));

    while(ch[i]!=' '){
        lc1[i]=ch[i];
        printf("\nin loop with lc1[i] = %c and ch[i] =  %c",lc1[i],ch[i]);
        i++;
    }
    lc1[i]='\0';
    i++;
    while(ch[i]!=' '){
        lc2[j]=ch[i];
        printf("\nin loop with lc2[j] = %c and ch[i] =  %c",lc2[j],ch[i]);
        j++;
        i++;
    }
    lc2[j]='\0';
    i++;
    *num=atoi(&ch[i]);

    *part1=lc1;
    *part2=lc2;

    printf("\nsplit results are:\n");
    printf("part1=%s and part2=%s and num=%d and lc1=%s lc2=%s    //this is surprising me",*part1,*part2,*num,lc1,lc2);

}

int main()
{
    int N,i,j,n,*numArray,count=0;
    char **arr,*part1,*part2,*token;
    scanf("%d",&N);
    arr=malloc(N*sizeof **arr);
    numArray=malloc(N*sizeof *numArray);
    for(i=0;i<N;i++){
    arr[i]=(char *)malloc(50*sizeof(char));
    }

    for(i=0;i<N;i++){
        printf("plz enter %d th :",i);
        scanf(" ");
        gets(&arr[i][0]);
    }

    for(i=0;i<N;i++){
        printf("%s",arr[i]);
    }

    for(i=0;i<N;i++){
    /*token=strtok(arr[i]," ");
    part1=token;
    token=strtok(NULL," ");
    part2=token;
    token=strtok(NULL," ");
    n=atoi(token);*/
        split(arr[i],&part1,&part2,&n);
    //some logic to use part1 and part2 of the sentence
}
return 0;

}

我提供的输入如下：

1
abcd efgh 2

输入的第一行包含我想要继续的句子数。我得到的输出如下：

plz enter 0 th :abcd efgh 2value of length is 11
this function recieved abcd efgh 2 for splitting into pieces

in loop with lc1[i] = a and ch[i] =  a
in loop with lc1[i] = b and ch[i] =  b
in loop with lc1[i] = c and ch[i] =  c
in loop with lc1[i] = d and ch[i] =  d
in loop with lc2[j] = e and ch[i] =  e
in loop with lc2[j] = f and ch[i] =  f
in loop with lc2[j] = g and ch[i] =  g
in loop with lc2[j] = h and ch[i] =  h
split results are:
part1=a and part2=e and num=2 and lc1=a lc2=e    //this is surprising me
Success time: 0 memory: 2296 signal:0
plz enter 0 th :abcd efgh 2value of length is 11
this function recieved abcd efgh 2 for splitting into pieces

in loop with lc1[i] = a and ch[i] =  a
in loop with lc1[i] = b and ch[i] =  b
in loop with lc1[i] = c and ch[i] =  c
in loop with lc1[i] = d and ch[i] =  d
in loop with lc2[j] = e and ch[i] =  e
in loop with lc2[j] = f and ch[i] =  f
in loop with lc2[j] = g and ch[i] =  g
in loop with lc2[j] = h and ch[i] =  h
split results are:
part1=a and part2=e and num=2 and lc1=a lc2=e    //this is surprising me

虽然split（）中的循环函数正在成功执行字符串中的所有字符，但我只得到part1（也在lc1中）和part2（也在lc2中）中的字符。这个输出的原因是什么？

Answer 1

这一行错了：

arr=malloc(N*sizeof **arr);

它应该是：

arr=malloc(N*sizeof *arr);

**arr是char，所以它只为N个字节分配空间，但是你需要N个指针的空间，这个指针是4个字节。所以你没有分配足够的空间，然后你在数组边界外写字，导致未定义的行为。

DEMO

为什么字符指针只被分配一个字符，而一个字符串应该被分配给它？

1 个答案: