C语言字符串函数模拟实现流程介绍

#include <stdio.h>
#include <assert.h>
size_t my_strlen(const char* str)
{
	assert(str);//断言一下传过来的参数是否为空指针
	size_t count = 0;//设置一个计数器
	while (*str++)
	{
		count++;
	}
	return count;
}
int main()
{
	char arr[] = "hello world!";
	int ret = my_strlen(arr);
	printf("%d\n", ret);
	return 0;
}

#include <stdio.h>
#include <assert.h>
size_t my_strlen(const char* str)
{
	assert(str);
	if (*str != '\0')
		return 1 + my_strlen(str + 1);
	else
		return 0;
}
int main()
{
	char arr[] = "hello world!";
	int ret = my_strlen(arr);
	printf("%d\n", ret);
	return 0;
}

#include <stdio.h>
#include <assert.h>
size_t my_strlen(const char* str)
{
	assert(str);
	const char* start = str;
	const char* end = str;
	while (*end != '\0')
	{
		end++;
	}
	return end - start;
}
int main()
{
	char arr[] = "hello world!";
	int ret = my_strlen(arr);
	printf("%d\n", ret);
	return 0;
}

#include <stdio.h>
#include <assert.h>
char* my_strcpy(char* dest, const char* scr)
{
	assert(dest);
	assert(scr);
	char* start = dest;//记录目标指针的起始位置
	while (*dest++ = *scr++)
	{
		;
	}
	return start;
}
int main()
{
	char arr1[20] = "xxxxxxxxxxxxxxxxxxx";
	char arr2[] = "hello world!";
	printf("%s\n", my_strcpy(arr1, arr2));
	return 0;
}

#include <stdio.h>
#include <assert.h>
char* my_strcat(char* dest, const char* scr)
{
	assert(dest);
	assert(scr);
	char* start = dest;
	while (*dest != '\0')
	{
		dest++;//先将目标指针遍历到'\0'的位置上
	}
	while (*dest++ = *scr++)
	{
		;
	}
	return start;
}
int main()
{
	char arr1[20] = "hello ";
	char arr2[] = "world!";
	printf("%s\n", my_strcat(arr1, arr2));
	return 0;
}

#include <stdio.h>
#include <assert.h>
int my_strcmp(const char* str1, const char* str2)
{
	assert(str1);
	assert(str2);
	while (*str1 == *str2)
	{
		if (*str1 != '\0')//两个字符串对应元素相等并都不为'\0'时，遍历这个字符串
		{
			str1++;
			str2++;
		}
		else
			return 0;//此为直到两个字符串结束都相等，所以返回0
	}
	return *str1 - *str2;//不相等时返回两个字符串对应元素的差值即可判断大小。
}
int main()
{
	char arr1[] = "abc";
	char arr2[] = "abcd";
	int ret = my_strcmp(arr1, arr2);
	if (ret > 0)
	{
		printf("arr1>arr2\n");
	}
	else if (ret < 0)
	{
		printf("arr1<arr2\n");
	}
	else
		printf("arr1==arr2\n");
	return 0;
}