1、实现strstr函数
函数原型是char *strstr(char *str1,char *str2);作用是找出str2字符串在str1字符串中第一次出现的位置(不包括str2的串结束符) 如果找到返回该位置的指针。若找不到,返回NULL指针。
const char * pstrstr(const char *haystack, const char *needle) { const char *p1, *p2; p1 = haystack; p2 = needle; while (*haystack != '/0' && *needle != '/0') { if (*haystack++ != *needle++) { needle = p2; haystack = ++p1; //从下一个字符开始搜索needle } } if (*needle == '/0') return p1; return NULL; }
2、实现strcpy函数
char *strcpy(char *dest,char *src);
功能:把src所指由NULL结束的字符串复制到dest所指的数组中。
说明:src和dest所指内存区域不可以重叠且dest必须有足够的空间来容纳src的字符串。
src字符串尾的字符串结束标识符'/0'也会被复制过去,复制完成后s1中的内容会被覆盖掉
char * strcpy( char *strDest, const char *strSrc )
{
assert( (strDest != NULL) && (strSrc != NULL) );
char *address = strDest;
while( (*strDest++ = * strSrc++) != '/0' );
return address;
}
char *strncpy(char *strDes, const char *strSrc, unsigned int count)
{
assert(strDes != NULL && strSrc != NULL);
char *address = strDes;
while (count-- && *strSrc != '/0')
*strDes++ = *strSrc++;
*strDes = '/0';
return address;
}
//查找字符串s中首次出现字符c的位置
char *strchr(const char *str, int c)
{
assert(str != NULL);
for (; *str != (char)c; ++ str)
if (*str == '/0')
return NULL;
return str;
}
int strcmp(const char *s, const char *t)
{
assert(s != NULL && t != NULL);
while (*s && *t && *s == *t)
{
++ s;
++ t;
}
return (*s - *t);
}
char *strcat(char *strDes, const char *strSrc)
{
assert((strDes != NULL) && (strSrc != NULL));
char *address = strDes;
while (*strDes != '/0')
++ strDes;
while ((*strDes ++ = *strSrc ++) != '/0')
NULL;
return address;
}
int strlen(const char *str)
{
assert(str != NULL);
int len = 0;
while (*str ++ != '/0')
++ len;
return len;
}
//此函数,梦修改如下
char *strdup_(char *strSrc)
//将字符串拷贝到新的位置
{
if(strSrc!=NULL)
{
char *start=strSrc;
int len=0;
while(*strSrc++!='/0')
len++;
char *address=(char *)malloc(len+1);
assert(address != NULL);
while((*address++=*start++)!='/0');
return address-(len+1);
}
return NULL;
}
//多谢laoyi19861011指正
char *strstr(const char *strSrc, const char *str)
{
assert(strSrc != NULL && str != NULL);
const char *s = strSrc;
const char *t = str;
for (; *strSrc != '/0'; ++ strSrc)
{
for (s = strSrc, t = str; *t != '/0' && *s == *t; ++s, ++t)
NULL;
if (*t == '/0')
return (char *) strSrc;
}
return NULL;
}
char *strncpy(char *strDes, const char *strSrc, unsigned int count)
{
assert(strDes != NULL && strSrc != NULL);
char *address = strDes;
while (count -- && *strSrc != '/0')
*strDes ++ = *strSrc ++;
*strDes = '/0';
return address;
}
char *strncat(char *strDes, const char *strSrc, unsigned int count)
{
assert((strDes != NULL) && (strSrc != NULL));
char *address = strDes;
while (*strDes != '/0')
++ strDes;
while (count -- && *strSrc != '/0' )
*strDes ++ = *strSrc ++;
*strDes = '/0';
return address;
}
int strncmp(const char *s, const char *t, unsigned int count)
{
assert((s != NULL) && (t != NULL));
while (*s && *t && *s == *t && count --)
{
++ s;
++ t;
}
return (*s - *t);
}
char *strpbrk(const char *strSrc, const char *str)
{
assert((strSrc != NULL) && (str != NULL));
const char *s;
while (*strSrc != '/0')
{
s = str;
while (*s != '/0')
{
if (*strSrc == *s)
return (char *) strSrc;
++ s;
}
++ strSrc;
}
return NULL;
}
int strcspn(const char *strSrc, const char *str)
{
assert((strSrc != NULL) && (str != NULL));
const char *s;
const char *t = strSrc;
while (*t != '/0')
{
s = str;
while (*s != '/0')
{
if (*t == *s)
return t - strSrc;
++ s;
}
++ t;
}
return 0;
}
int strspn(const char *strSrc, const char *str)
{
assert((strSrc != NULL) && (str != NULL));
const char *s;
const char *t = strSrc;
while (*t != '/0')
{
s = str;
while (*s != '/0')
{
if (*t == *s)
break;
++ s;
}
if (*s == '/0')
return t - strSrc;
++ t;
}
return 0;
}
char *strrchr(const char *str, int c)
{
assert(str != NULL);
const char *s = str;
while (*s != '/0')
++ s;
for (-- s; *s != (char) c; -- s)
if (s == str)
return NULL;
return (char *) s;
}
char* strrev(char *str)
{
assert(str != NULL);
char *s = str, *t = str, c;
while (*t != '/0')
++ t;
for (-- t; s < t; ++ s, -- t)
{
c = *s;
*s = *t;
*t = c;
}
return str;
}
char *strnset(char *str, int c, unsigned int count)
{
assert(str != NULL);
char *s = str;
for (; *s != '/0' && s - str < count; ++ s)
*s = (char) c;
return str;
}
char *strset(char *str, int c)
{
assert(str != NULL);
char *s = str;
for (; *s != '/0'; ++ s)
*s = (char) c;
return str;
}
char *strtok(char *strToken, const char *str)
{
assert(strToken != NULL && str != NULL);
char *s = strToken;
const char *t = str;
while (*s != '/0')
{
t = str;
while (*t != '/0')
{
if (*s == *t)
{
*(strToken + (s - strToken)) = '/0';
return strToken;
}
++ t;
}
++ s;
}
return NULL;
}
char *strupr(char *str)
{
assert(str != NULL);
char *s = str;
while (*s != '/0')
{
if (*s >= 'a' && *s <= 'z')
*s -= 0x20;
s ++;
}
return str;
}
char *strlwr(char *str)
{
assert(str != NULL);
char *s = str;
while (*s != '/0')
{
if (*s >= 'A' && *s <= 'Z')
*s += 0x20;
s ++;
}
return str;
}
void *memcpy(void *dest, const void *src, unsigned int count)
{
assert((dest != NULL) && (src != NULL));
void *address = dest;
while (count --)
{
*(char *) dest = *(char *) src;
dest = (char *) dest + 1;
src = (char *) src + 1;
}
return address;
}
void *memccpy(void *dest, const void *src, int c, unsigned int count)
{
assert((dest != NULL) && (src != NULL));
while (count --)
{
*(char *) dest = *(char *) src;
if (* (char *) src == (char) c)
return ((char *)dest + 1);
dest = (char *) dest + 1;
src = (char *) src + 1;
}
return NULL;
}
void *memchr(const void *buf, int c, unsigned int count)
{
assert(buf != NULL);
while (count --)
{
if (*(char *) buf == c)
return (void *) buf;
buf = (char *) buf + 1;
}
return NULL;
}
int memcmp(const void *s, const void *t, unsigned int count)
{
assert((s != NULL) && (t != NULL));
while (*(char *) s && *(char *) t && *(char *) s == *(char *) t && count --)
{
s = (char *) s + 1;
t = (char *) t + 1;
}
return (*(char *) s - *(char *) t);
}
void *memmove(void *dest, const void *src, unsigned int count)
{
assert(dest != NULL && src != NULL);
char* pdest = (char*) dest;
char* psrc = (char*) src;
//pdest在psrc后面,且两者距离小于count时,从尾部开始移动. 其他情况从头部开始移动
if (pdest > psrc && pdest - psrc < count)
{
while (count--)
{
*(pdest + count) = *(psrc + count);
}
} else
{
while (count--)
{
*pdest++ = *psrc++;
}
}
return dest;
}
void *memset(void *str, int c, unsigned int count)
{
assert(str != NULL);
void *s = str;
while (count --)
{
*(char *) s = (char) c;
s = (char *) s + 1;
}
return str;
}