字符串操作——C语言实现

代码如下： 

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

char ch1[]={ 'c', '+', '+'};
char ch2[]={ 'c', '+', '+', '\0'};
char ch3[] = "myC++";
char ch4[] = "good idea";

int strlen_new(const char* src);//const 2'
char* strcat_new(char *strD, const char *strS);
char* strcpy_new(char *strD, const char *strS);
int strcmp_new(const char *s1, const char *s2);
void* memcpy_new(void* dst, void* src, size_t n);
void* memmove_new(void* dst, void* src, size_t n);

void* memmove_new(void* dst, void* src, size_t n)
{
	char * dp = (char*)dst;
	char * sp = (char*)src;
	assert(src != NULL && dst != NULL && n>0);
	if(sp > dp || (sp + n) < dp)
	{
		while(n--)
		{
			*(dp++)=*(sp++);
		}
		*dp='\0';
	}
	else if (sp < dp)
	{
        sp += n;
        dp += n;
        *dp = '\0';
    	while(n--)
        	*(--dp) = *(--sp);
	}
    return dst;
}

void* memcpy_new(void* dst, void* src, size_t n)
{
	char* dp = (char*)dst;
	char* sp = (char*)src;
	assert(src != NULL && dst != NULL && n>0);
	while(n--)
	{
		*dp = *sp;
		dp++;
		sp++;
	}
	dp = '\0';
	return dst;
}

int strlen_new(const char* src)
{
	int count = 0;
	assert(src != NULL);
	while(*src++ != '\0')
	{
		count++;
	}

	return count;
}

char * strcat_new(char * strD, const char * strS)
{
	char * add = strD;
	assert(strD != NULL && strS != NULL);

	while(*strD != '\0')
		strD++;
	while((*strS) != '\0')
	{
		*strD = *strS;
		strD++;
		strS++;
	}
	*strD = '\0';

	//while(*strD++ = *strS++);//cat  more efficient

	return add;
}

char* strcpy_new(char *strD, const char *strS)
{
	char * add = strD;
	assert(strD != NULL && strS != NULL);

	while(*strS != '\0')
		*strD++ = *strS++;

//attention姝ゅ锛岃嫢*strS涓衡€橽0鈥橈紝鍒欏叾鍏堣祴鍊肩粰strD锛屾晠鏈€鍚庝笉闇€瑕佸啀娣诲姞'\0'
//while(*strD++ = *strS++);

	*strD = '\0';

	return add;
}

int strcmp_new(const char *s1, const char *s2)
{
	//int ret;
	assert(s1 != NULL && s2 != NULL);

	while(*s1 && *s2 && *s1 == *s2)
	{
		s1++;
		s2++;
	}
	return *s1 - *s2;
	//return *s2 - *s1;
}

int main ()
{
	int str_len = 0;

	char* mem_src = "the src test memcpy";
	char mem_dest[29] = "another hello";
	char* mv_src = "the src test memmove";
	char mv_dest[20];
    printf("Test memcpy ret is :%s\n", memcpy(mem_dest, mem_src, 20));
    printf("Test memmove ret is :%s\n", memmove_new(mv_dest, mv_src, 10));

	str_len = strlen_new(ch3);

	//printf("%s\n", strcat_new(ch3, ch4));

	printf("%s\n", strcpy_new(ch3,ch4));

	printf("strcmp = %d\n", strcmp_new(ch3,ch4));

	printf("len = %d ,%s\n", str_len, ch3);
	return 0;
}

运行结果如下：

Test memcpy ret is :the src test memcpy
Test memmove ret is :the src te
good idea
strcmp = 6
len = 5 ,good idea

Process returned 0 (0x0)   execution time : 0.047 s
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