字符串函数的模拟实现

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strchr( char *dest, const char src){
	while (*dest++){
		if (*dest == src)
			return dest;

	}
	return NULL;

}
int main(){
	char arr[20] = "abcddddef";
	char a = 'd';
    char *ret = 0;
	ret =  my_strchr(arr, a);
	printf("%s\n",ret);
	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strrchr(char *dest,const char src){
	char *temp = NULL;
	while (*dest++)
	{
		if (*dest == src)
			temp = dest;
	}
	return temp;
}
int main(){
	char arr[20] = "asddddddf";
	char a = 'd';
	char *ret = 0;
	ret = my_strrchr(arr, a);
	printf("%s\n",ret);
	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
int my_strncmp(const char *s1,const char *s2,size_t n){
	assert(s1 != NULL);
    assert(s2 != NULL);
	while (n--){
		if ((*s1 == *s2)&&*s1){
			s1++;
			s2++;
		}
		else if (*s1 != *s2)
		{
			return (*(unsigned char*)s1 - *(unsigned char*)s2);
		}
	}
	return 0;
}
int main(){
	char *s1 = "wangmazi";
	char *s2 = "wisi";
	
		printf("%d\n", my_strncmp(s1, s2, 2));
		
	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
int my_strcmp(const char* s1, const char* s2)
{
	assert(s1);
	assert(s2);
	while ((*s1 == *s2)&&*s1)
	{
		++s1;
		++s2;
	}
	return  (*(unsigned char*)s1 - *(unsigned char*)s2);
}
int main()
{
	char *p = "abcdef";
	char arr[] = "abcdef";
	if (my_strcmp(p, arr) < 0)
	{
		printf("%s\n", p);
	}
	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
char* my_strcat(char* dest,const char* src)
{
	assert(dest != NULL);
	assert(src != NULL);
	char* ret = dest;
	while (*dest)
	{
		++dest;
	}
	while (*dest++ = *src++)
	{
		;
	}
	return ret;
}
int main()
{
	char arr[20] = "week";
	char *p = "end";
	printf("%s\n", my_strcat(arr, p));

	system("pause");
	return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
char *my_strncat(char *dest,const char *src,size_t n){
	assert(dest!=NULL);
	assert(src!=NULL);
	char *s1 = dest;
	while (*dest){
		++dest;
	}
	while (n--){
		*dest++ = *src++;
	}
	return s1;
}
int main(){
	char arr[20] = "week";
	char *p = "end";
	my_strncat(arr, p, 2);
	
	printf("%s\n",arr);
	system("pause");
	return 0;
}


#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
char* my_strcpy(char *dest, const char* src)
{
	assert(dest);
	assert(src);
	char* ret = dest;
	while (*dest++ = *src++)
	{
		;
	}
	return ret;
}
int main()
{
	char arr[20] = { 0 };
	char* p = "hello world";
	printf("%s\n", my_strcpy(arr, p));
	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

char *my_strncpy(char *dest,const char*src,size_t n){
	assert(dest!=NULL);
	assert(src!=NULL);
	char *s1 = dest;
	while ((n) && *src)
	{
			*dest++ = *src++;
			n--;
	}
	if (n)
	{
		while (--n)
		{
			*dest++ = '\0';
		}
	}
	return s1;
}
int main(){
	char arr[20] = { 0 };
	char *p = "asddd";
	my_strncpy(arr, p, 3);
	printf("%s\n",arr);

	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
int my_strlen(const char* src)
{
	assert(src);
	int count = 0;
	while (*src++)
	{
		count++;
	}
	return count;
}
int main()
{  
	printf("%d\n", my_strlen("abcdef"));

	system("pause");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
int my_strlen(const char* src)
{
	if (*src)
	{
		return (1 + my_strlen(src + 1));
	}
	else
	{
		return 0;
	}
}
int main()
{
	printf("%d\n", my_strlen("abcdef"));
	system("pause");
	return 0;
}

#include <stdlib.h>
#include <string.h>
#include <assert.h>
char* my_strstr(char* dest, const char* src)
{
	assert(dest != NULL);
	char* cur = dest;
	const char* ptr = src;
	while (*dest++)
	{
		cur = dest;
		while (*cur == *ptr)
		{
			++cur;
			++ptr;
		}
		if (*ptr == '\0')
		{
			return dest;
		}
		else
		{
			ptr = src;
		}
	}
	return NULL;
}
int main()
{
	char* p = "abbbbcdef";
	char arr[] = "g";
	printf("%s\n", my_strstr(p, arr));
	system("pause");
	return 0;
}