strtok() 函数的实现 [英] Implementation of strtok() function

问题描述

我需要编写我的函数strtok.下面是我的代码.问题是 - 我无法显示结果字符串.在代码中，我使用 strcpy() 然后显示新数组.是否可以仅使用指针 *str 来显示字符串?

I need to write my function strtok. Below is my code. The problem is - I can't display result string. In code I use strcpy() and then display new array. Is it possible to display string using just pointer *str?

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

char* my_strtok(char* s, char* delm){
    char W[100];
    int i = 0, k = 0, j = 0;
    char *ptr;
    static char *Iterator;
    ptr = s;

    if (s == NULL){
        s = Iterator;
    }
    while (s[i] != '\0'){
        j = 0;
        while (delm[j] != '\0'){
            if (s[i] != delm[j])
                W[k] = s[i];
            else goto It;
            j++;
        }
        ptr++;
        i++;
        k++;
    }
It:
    W[i] = 0;
    Iterator = ++ptr;
    return W;
}

int main(void){
    char s[100];
    char delm[] = " ";
    gets(s);
    char newstr[100];
    char *str = my_strtok(s, delm);
    strcpy(newstr, str);
    printf("%s", newstr);
    return 0;
}

推荐答案

strtok 的内部实现已经在这里讨论过:

Internal implementation of strtok has already been discussed here:

strtok() 如何将字符串拆分为C 中的标记?

在您的实现类型中(称其为您的类型，因为它与实际的完全不同)，您没有为局部变量W"动态分配任何内存.因此，当您返回它时，不能保证您会正确接收字符串，因为在调用函数中不再为其保留本地分配给 'W' 的内存.除此之外，代码中还使用了许多不必要的变量.而且，它需要适当的重组.为了您更好地理解，我已经修改了您的代码(尽可能保持您的风格)以完成所需的工作:

In your type of implementation ( calling it your type because it is quite different from the actual one), you have not allocated any memory dynamically to the local variable 'W'. So when you return it, it is not guaranteed that you will receive the string correctly because that memory which was locally allocated to 'W' is not reserved for it anymore in the calling function. Apart from this, there are many unnecessary variables used in the code. And also, it needs proper re-structuring. For your better understanding I have modified your code(keeping it in your style as far as possible) to do the required job:

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

char* my_strtok(char* s, char* delm)
{
    static int currIndex = 0;
    if(!s || !delm || s[currIndex] == '\0')
    return NULL;
    char *W = (char *)malloc(sizeof(char)*100);
    int i = currIndex, k = 0, j = 0;

    while (s[i] != '\0'){
        j = 0;
        while (delm[j] != '\0'){
            if (s[i] != delm[j])
                W[k] = s[i];
            else goto It;
            j++;
        }

        i++;
        k++;
    }
It:
    W[i] = 0;
    currIndex = i+1;
    //Iterator = ++ptr;
    return W;
}

int main(void)
{
    char s[100] = "my name is khan";
    char delm[] = " ";
    //char newstr[100];
    char *str = my_strtok(s, delm);
    while(str){
        printf("%s", str);
        free(str);
        str = my_strtok(s, delm);
    }

    return 0;
}

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