如何实现字符指针数组函数？

Question

我尝试编写一个函数，该函数返回字符串的副本，其中带前导字符和尾随字符，这些字符存储在“字符”中。例如：

  strip("-__-ceng_240---__,," , "_-,") 

  return "ceng_240"

这是我的代码，但不起作用。我想我有点小问题，但我找不到。

char* strip(char* string, char* characters) {

    int i,j,k=0;

    char* astring = malloc((strlen(string)+1));

    for(i=0;string[i]!='\0';i++) {
        for(j=0;characters[j]!='\0';j++) {
            if(string[i]==characters[j])
                continue;
            else if(string[i]!=characters[j]) {
                astring[k] = string[i];
                k++;
                break;
            }
        }
    }
    astring[k] = '\0';
    astring = realloc(astring,strlen(astring));

    return astring;
}

Answer 1

我把这个trim==修剪称为左&右修剪，就像这个工作样例：

#include <stdio.h> 

char* trim_left(char* s, char* p) {
    char*q;
    while (*s){
        q = p;
        while (*q){
            if (*s != *q)q++; else { s++; break; }
        }
        if (!*q)break;
    }
    return s;
}
char* trim_right(char* s, char* p) {
    char *r = s;
    char*q;
    while (*s) s++;
    s--;
    while (s != r){
        q = p;
        while (*q){
            if (*s != *q)q++; else { s--; break; }
        }
        if (!*q)break;
    }
    s++;
    *s = 0;
    return r;
}
char* trim(char* s, char* p) {
    return  trim_left(trim_right(s, p), p);
}

int main(){
    char str[] = "-__-ceng_240---__,,";
    char *p = trim(str, "_-,");
    printf("%s", p); //ceng_240
    //return "ceng_240"
}

另一种使用助手函数is_trimchar的方法：

#include <stdio.h> 

char trim_chars[] = "_-,";

int is_trimchar(char c){
    char *p = trim_chars;
    do{
        if (*p == c)return 1;
        p++;
    } while (*p);
    return 0;
}


char* trim_left(char* s) {
    while (*s)
        if (is_trimchar(*s)) s++; else break;
    return s;
}

char* trim_right(char* s) {
    char *r = s;
    while (*s) s++;
    s--;
    while (s != r)
        if (is_trimchar(*s)) s--; else break;
    s++;
    *s = 0;
    return r;
}

char* trim(char* s) {
    return  trim_left(trim_right(s));
}

int main(){
    char str[] = "-__-ceng_240---__,,";
    char *p = trim(str);
    printf("%s", p); //ceng_240
    //return "ceng_240"
}

Answer 2

尝试:char* astring =(char*)malloc(sizeof(char) * (strlen(string)+1))；

Answer 3

试试这个：

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

char* strip(char* string, char* characters) {
    int i, j, k;
    char *p = string + strspn(string, characters);//skip front
    char *astring = malloc(strlen(p)+1);

    for(j=i=0; p[i] != '\0'; i++) {
        astring[j++] = p[i];//copy
    }
    astring[j] = '\0';
    for(k = j -1; k >= 0; --k){//delete from tail
        if(strchr(characters, astring[k]))
            astring[k] = '\0';
        else
            break;
    }
    astring = realloc(astring, strlen(astring) + 1);//need +1
    return astring;
}
int main(void){
    char *result = strip("-__-ceng_240---__,," , "_-,");
    printf("'%s'\n", result);
    free(result);
    return 0;
}