字符串操作函数实现

一直觉得自己眼高手低, 平时也懒得写代码, 下定决心要克服这个毛病,于是开始了重新拿起 the c programming languages 这本C语言圣经做做上面的练习题.就当是练手吧.

这次从字符串操作部分入手,实现自己的库,争取多写,多思考.而后看看一下coreutilities的GNU和NetBSD实现,接着看看(e)glibc,再以后,再打算吧.希望能有高手指出自己的不足,提高自己,一切以学习为目的.

/*
 * =====================================================================
 *
 *       Filename:  wolf_string.c
 *
 *    Description:  Defination for my str lib
 *
 *        Version:  1.0
 *        Created:  2011年09月01日 13时14分35秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  wolfpython(walter) (), [e-mail]
 *        Company:
 *
 * ====================================================================
 */
#include "wolf_string.h"
#include <assert.h>


int
wolf_strlen(char *src)
{
    int i = 0;

    while(*src != '\0') {
        src++;
        i++;
    }

    return i;
}

int
wolf_strlen_1(char *src)
{
    char *p = src;

    while(*src != '\0')
        src++;

    return src-p;
}

void
wolf_strcpy(char *des, char *src)
{
    /* if des is a null pointer, its not safe to modify the mem
     * if the src is a null pointer, it doesnt make any sense
     * */
    assert(des != NULL && src != NULL);

    while((*des = *src) != '\0') {
        des++;
        src++;
    }
}


void
wolf_strcpy_1(char *des, char *src)
{
        /* if des is a null pointer, its not safe to modify the mem
     * if the src is a null pointer, it doesnt make any sense
     * */
    assert(des != NULL && src != NULL);

    while(*des++ = *src++)
        ;
}


int
wolf_strcmp(char *des, char *src)
{
    /* if des is a null pointer, its not safe to modify the mem
     * if the src is a null pointer, it doesnt make any sense
     * */
    assert(des != NULL && src != NULL);

    while(*des == *src) {
        if(*des == '\0') {
            return 0;
        }

        des++;
        src++;
    }

    return *des - *src;
}


void
wolf_strcat(char *des, char *src)
{
    /* it doesnt matter if the src is a null pointer */
    assert(des != NULL);

    while(*des != '\0')
        des++;

    while(*des++ = *src++)
        ;
}

/*
 *if t is at the end of s, return 1,
 *else return 0
 * */
int
wolf_strend(char *s, char *t)
{
    int tsize;
    char *thead = t;             // the head of t

    /* it doesnt make any sense if t is a null pointer */
    assert(t != NULL);

    if( s == NULL) return 0;
    while(*s != '\0')
        s++;

    while(*t != '\0')
        t++;
    tsize = t - thead;

    while(tsize-- > 0) {
        if(*s != *t)
            return 0;
        s--;
        t--;
    }

    return 1;
}