字符串操作实现（C语言版本）

/获取字符串长度**************/
int mystrlen (const char *str)
{
char *s = (char *)str;
int len = 0;

if (s == NULL)
    return 0;

while (*s++ != '\0')
    ++len;

return len;

}

/字符串拼接***********/
char * mystrcat (char *dest, const char *src)
{
char *dp;
char *sp = (char *)src;

if ((dest != NULL) && (src != NULL))
{
    dp = &dest[mystrlen(dest)];

    while (*sp != '\0')
    {
        *dp++ = *sp++;
    }
    *dp = '\0';
}
return dest;

}

/字符串前n项拼接**************/
char * mystrncat (char *dest, const char *src, int n)
{
char *dp;
char *sp = (char *)src;

if ((dest != NULL) && (src != NULL) && (n > 0))
{
    dp = &dest[mystrlen(dest)];

    while ((*sp != '\0') && (n-- > 0))
    {
        *dp++ = *sp++;
    }
    *dp = '\0';
}
return dest;

}

/字符串拷贝**********/
char * mystrcpy (char *dest, const char *src)
{
char *dp = (char *)dest;
char *sp = (char *)src;

if ((dest != NULL) && (src != NULL))
{
    while (*sp != '\0')
    {
        *dp++ = *sp++;
    }
    *dp = '\0';
}
return dest;

}

/字符串前n项拷贝********/
char * mystrncpy (char *dest, const char *src, int n)
{
char *dp = (char *)dest;
char *sp = (char *)src;

if ((dest != NULL) && (src != NULL) && (n > 0))
{
    while ((*sp != '\0') && (n-- > 0))
    {
        *dp++ = *sp++;
    }
    *dp = '\0';
}
return dest;

}

/字符串比较，一致返回0****************/
int mystrcmp (const char *s1, const char s2)
{
/ No checks for NULL */
char *s1p = (char *)s1;
char *s2p = (char *)s2;

while (*s2p != '\0')
{
    if (*s1p != *s2p)
        break;

    ++s1p;
    ++s2p;
}
return (*s1p - *s2p);

}

/字符串前n项比较，一致返回0****************/
int mystrncmp (const char *s1, const char s2, int n)
{
/ No checks for NULL */
char *s1p = (char *)s1;
char *s2p = (char *)s2;

if (n <= 0)
    return 0;

while (*s2p != '\0')
{
    if (*s1p != *s2p)
        break;

    if (--n == 0)
        break;

    ++s1p;
    ++s2p;
}
return (*s1p - *s2p);

}

/设置一定内存区域n长度内容为c形参**********/
void * mymemset (void s, int c, unsigned n)
{
/ Not optimized, but very portable */
uint8 *sp = (uint8 *)s;

if ((s != NULL) && (n > 0))
{
    while (n--)
    {
        *sp++ = (uint8)c;
    }
}
return s;

}

/内存拷贝**/
void *mymemcpy(void *des,const void *src,size_t len)
{
char * result =des;
const char * from = src;
//assert(des&&src);
while(len–)
{
*(result++) = *(from++);
}
return des;
}

char *strchr(const char *s, int c) {
const char c_ = (char)c;
do {
if (*s == c_) {
return (char *)s;
}
} while (*s++ != ‘\0’);
return NULL;
}

size_t strcspn(const char *s1, const char *s2) {
size_t res = 0;
while (*s1 != ‘\0’) {
if (strchr(s2, *s1) == NULL) {
++s1;
++res;
} else {
return res;
}
}
return res;
}

/把s字符串用delim分割，用法例子在下面****/
char *mystrtok(char *s, const char *delim) {
static char *last;

if (s == NULL) {
    s = last;
}
int ch;
do {
    ch = *s++;
    if (ch == '\0') {
        return NULL;
    }
} while (strchr(delim, ch));
--s;
last = s + strcspn(s, delim);
if (*last != '\0') {
    *last++ = '\0';
}
return s;

}
/*用法例：
char *buf4tok,i; //保存当前tok和计数
char srt_buf[50] = {"a,bc,d-ef,1 23,!,@a aa,\n,ee-e,@#$^&,ww, "}; //要用’,‘或者’ ‘或者’-'分割的字符串

buf4tok = mystrtok(srt_buf," ,-"); //先调用一次，获取第一个tok
if(buf4tok != NULL)
{
    for(i = 0;buf4tok != NULL;i++)
    {
        printf("%3d : %s\r\n",i,buf4tok);
        buf4tok = mystrtok(NULL," ,-"); //然后循环调用，第二次和之后都填入NULL，每次调用都返回接下来的tok，直到返回NULL为止
    }
}

*/