常用的字符串函数-2

字符串常用函数

myitoa

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

void resver(char *s)//反转字符串  
{  
    int len = strlen(s);  
    //printf("len=%d\n",len);  
    int i = 0;  
    char tmp = 0;  
    for (; i<len/2; i++)  
    {  
        tmp = s[i];  
        s[i] = s[len-1-i];  
        s[len-1-i] = tmp;  
    }  
}  

const char *myitoa(int n)  
{  
    static char buf[100];//必须为static,或者是全局变量  
    memset(buf, 0, sizeof(buf));  
    int FlagF = 0;    //1-f, 0-z  
    int i = 0;  
    if (n < 0)  
    {  
        FlagF = 1;  
        n = 0 - n;  
    }  
    while (n)  
    {  
        buf[i++] = n % 10 + '0';  
        n = n / 10;  
    }  
    if (FlagF == 1)  
    {  
        buf[i++] = '-';  
    }  
    buf[i] = '\0';  
    printf("before buf:%s\n", buf);  
    resver(buf);  
    printf("after buf:%s\n", buf);  
    return buf;  
}  

int main()  
{  
    printf("%s\n", myitoa(123));  
    printf("%s\n", myitoa(-123));  
    return 0;  
}

myatoi

#include <stdio.h>  
int mystrlen(const char *s)  
{  
    int i = 0;  
    while (*s++)  
    {  
        i++;  
    }  
    return i;  
}  
int power10(int n)  
{  
    if (n == 0)  
    {  
        return 1;  
    }  
    int val = 1;  
    int i = 0;  
    for (; i < n; i++)  
    {  
        val = val * 10;  
    }  
    return val;  
}  
int char2i(char c)  
{  
    if ((c >= '0') || (c <= '9'))  
    {  
        return (c - '0');  
    } else  
    {  
        return 0;  
    }  
}  
int myatoi(const char *str)  
{  
    int FlagF = 0; //1-f, 0-z  
    const char *p = str;  
    int i = 0;  
    int value = 0;  
    if (str[0] == '-')  
    {  
        FlagF = 1;
        p = ++str;  
    }  
    int len = mystrlen(p);  
    int lentmp = len;  
    for (; i < len; i++)  
    {  
        value += char2i(p[i]) * power10(lentmp - 1);  
        lentmp--;  
    }  
    if (FlagF == 1)  
    {  
        return (0 - value);  
    } else  
    {  
        return value;  
    }  
}  

int main()  
{  
    const char *s = "-123";  
    printf("%d\n", myatoi(s));  
    return 0;  
}

常用的字符处理函数