① strlen(字符串长度)
size_t strlen (const char* str);
//计数器方式
int my_strlen(const char* str)
{
int count = 0;
assert(str != NULL);
while(*str++ != '\0')
{
count++;
}
return count;
}
//递归实现
int my_strlen(const char* str)
{
if(*str == '\0')
{
return 0;
}
else
{
return 1+my_strlen(str+1);
}
}
//指针实现
int my_strlen(char* s)
{
char* p = s;
while(*p != '\0')
{
p++;
}
return p-s;
}
② strcpy(字符串拷贝)
char* strcpy(char* des, const char* str);
char* my_strcpy(char* des,const char* str)
{
char* ret = des;
assert(des != NULL);
assert(str != NULL);
while(*des++ = *str++)
{
;
}
return ret;
}
③ strncpy(字符串拷贝n个)
char* strncpy(char* des, const char* str, size_t num);
char* my_strncpy(char* dest, const char* src, size_t num)
{
char* ret = dest;
assert(dest != NULL);
assert(src != NULL);
while (num--)
{
if (*src != '\0')
{
*dest = *src;
dest++;
src++;
}
else
{
*dest = 0;
dest++;
}
}
return ret;
}
④ strcat(字符串追加)
char* strcat(char* dest, const char* str);
char* my_strcat(char* dest, const char* str)
{
char* ret = dest;
assert(dest != NULL);
assert(str != NULL);
//找到目标空间的'\0'
while(*dest)
{
dest++;
}
//拷贝
while(*dest++ = *str++)
{
;
}
return ret;
}
⑤ strncat(字符串追加n个)
char* strncat(char* dest, const char* str, size_t num);
char* my_strncat(char* dest, const char* str, size_t num)
{
char* ret = dest;
assert(dest != NULL);
assert(str != NULL);
while(*dest++)
;
while(num--)
{
*dest++ = *str++;
}
return ret;
}
⑥ strcmp(字符串比较)
int strcmp(const char* str1, const char*str2);
int my_strcmp(const char* str1, const char*str2)
{
assert(str1 != NULL);
assert(str2 != NULL);
while(*str1 == *str2)
{
if(*str1 == '\0')
{
return 0;
}
str1++;
str2++;
}
return *str1 - *str2;
}
⑦ strncmp(字符串比较n个)
int strncmp(const char* str1, const char*str2, size_t num);
比较到出现两个字符不一样,或者一个字符串结束,或者num个字符全部比较完
int my_strncmp(const char* dest,const char* src,size_t num)
{
int ret = 0;
while (num--)
{
if (src == '\0')
return 0;
if (!(*dest == *src))
{
ret = *(unsigned char*)dest - *(unsigned char*)src;
}
dest++;
src++;
}
return ret;
}
⑧ strstr(找子字符串)
char* strstr(const char* str1, const char* str2);
返回str2第一次在str1中出现的一个指针,若str2没有在str1中出现则返回空指针
char* my_strstr(const char* str1, const char* str2)
{
const char* cur = str1;
const char* s1 = str1;
const char* s2 = str2;
assert(str1 != NULL);
assert(str2 != NULL);
while (*cur)
{
s1 = cur;
s2 = str2;
while ((*s1)&&(*s2)&&(*s1 == *s2))
{
s1++;
s2++;
}
if (*s2 == '\0')
{
return (char*)cur;
}
cur++;
}
return NULL;
}
⑨ memcpy
void* memcpy(void* dest,const void* src, size_t num);
//void*接收任意类型数据,void*不能解引用,不能自增自减
void* my_memcpy(void* dest,const void* src, size_t num)
{
void* ret = dest;
assert(dest != NULL);
assert(src != NULL);
//一个字节一个字节拷贝
while(num--)
{
*(char*)dest = *(char*)src;
dest = (char*)dest+1;
src = (char*)src+1;
}
return ret;
}
⑩ memmove
void* memmove(void* dest,const void* src,size_t num);
//方式一
void* my_memmove(void* dest,const void* src,size_t num)
{
void* ret = dest;
assert(dest != NULL);
assert(src != NULL);
if (dest < src)//前->后
{
while (num--)
{
*(char*)dest = *(char*)src;
dest = (char*)dest + 1;
src = (char*)src + 1;
}
}
else //后->前
{
while (num--)
{
*((char*)dest + num) = *((char*)src + num);
}
}
return ret;
}
//方式二
void* my_memmove(void* dest,const void* src,size_t num)
{
void* ret = dest;
assert(dest != NULL);
assert(src != NULL);
if (dest>src && dest<(char*)src+num)//后->前
{
while (num--)
{
*((char*)dest + num) = *((char*)src + num);
}
}
else //前->后
{
while (num--)
{
*(char*)dest = *(char*)src;
dest = (char*)dest + 1;
src = (char*)src + 1;
}
}
return ret;
}