相关头文件

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

数字转字符串

//num_str 由用户手动分配
int str_to_num(char *num_str){
    
    //atoi()只针对整数int，相应的有atof(),atol(),atoll(),自查
    int num = atoi(num_str);
    return num;
}

字符串转数字

char * num_to_str(int num){
    
    //itoa(int i) 在Linux或unix不存在
    char *buf = malloc(sizeof(num));
    //一般我用这种方式
    sprintf(buf, "%d",num);
    /*
    //10代表十进制
    char *num_str = gcvt(num, 10, buf);
    return num_str;
    */
    
    free(buf);
    return buf;
    
    
}

字符串连接

char * contact_str(char *s1,char *s2){
    unsigned long s1_len = strlen(s1);
    unsigned long s2_len = strlen(s2);
    unsigned long re_len = s1_len + s2_len;
    char *buf = (char *)malloc(re_len+1);
    /*
    for (int i = 0; i<s1_len; i++) {
        buf[i] = s1[i];
    }
    for (int i = 0; i<s2_len; i++) {
        buf[i+s1_len] = s2[i];
    }
     */
    
    memcpy(buf, s1, s1_len);
    memcpy(buf+s1_len, s2, s2_len);
    //不能在这里释放，要在外部释放
//    free(buf);
    
    return buf;
}

字符串子串

char *str_sub(char *s,int from,int len){
    if (s && strlen(s)) {
        s = s + from;
        char *sub = (char *)malloc(len+1);
        /*
        for (int i = 0; i<len; i++) {
            //printf("%c\n",s[from+i]);
            sub[i] = s[from+i];
        }
        */
        memcpy(sub, s, len);
        //不能在这里释放，要在外部释放
//        free(sub);
        return sub;
    }
    return NULL;
}