库函数的模拟实现(strlen)(strcpy)(strcat)(strcmp)(strstr)(memcpy)(memmove)(C语言)(VS)

---

前言

  这是我对库函数的模拟实现，希望对大家有帮助。

---

一、模拟实现strlen

---

---

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

size_t my_strlen(const char* str)
{
    
	assert(str);
	int tmp = 0;
	while (*str)
	{
    
		tmp++;
		str++;
	}
	if (!tmp)
		return NULL;
	return tmp;
}

二、模拟实现strcpy

---

---

char* my_strcpy(char* strDestination, const char* strSource)
{
    
	assert(strDestination&& strSource);
	char* tmp_strDestination = strDestination;
	while (*strDestination++ = *strSource++);
	return tmp_strDestination;
}

---

三、模拟实现strcat

---

---

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

char* my_strcat(char* strDestination, const char* strSource)
{
    
	assert(strDestination&& strSource);
	char* tmp_strDestination = strDestination;
	while (*strDestination++);
	strDestination--;
	while (*strDestination++ = *strSource++);
	return tmp_strDestination;
}

四、模拟实现strcmp

---

---

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

int my_strcmp(const char* string1, const char* string2)
{
    
	assert(string1 && string2);
	for (;;string1++, string2++)
	{
    
		if (*string1 == *string2 && *string2 == '\0')
			return 0;
		else if (*string1 == '\0' || *string1 < *string2)
			return -1;
		else if(*string2 == '\0' || *string1 > *string2)
			return 1;
	}
}

---

五、模拟实现strstr

---

---

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

char* my_strstr(const char* string, const char* strCharSet)
{
    
	assert(string && strCharSet);
	char* tmp_string = (char*)string;
	do
	if (*tmp_string == *strCharSet)
		return tmp_string;
	while (*tmp_string++);
	return NULL;
}

---

六、模拟实现memcpy

---

---

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

void* my_memcpy(void* dest, const void* src, size_t count)
{
    
	assert(dest && src);
	char* tmp_dest = dest;
	while (count--)
		*((char*)dest)++ = *((char*)src)++;
	return tmp_dest;
}

七、模拟实现memmove

---

---

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

void* my_memmove(void* dest, const void* src, size_t count)
{
    
	assert(dest && src);
	void* tmp_dest = dest;
	if (dest < src)
		while (count--)
			*((char*)dest)++ = *((char*)src)++;
	else
		while (count--)
			*((char*)dest + count) = *((char*)src + count);
	return dest;
}

七、看完记得给个三连，谢谢