程序员成长之旅——C语言模拟实现strchr和strstr

Mystrchr

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
char* Mystrchr(const char* str1, char str2)
{
	assert(str1);
	while (*str1)
	{
		if( *str1 == str2)
		{
			return (char*)str1;
		}
		str1++;
	}
	return NULL;
}
int main()
{
	char* str1 = "abcder";
	char str2 = 'b';
	char* ret = Mystrchr(str1, str2);
	printf("%s\n", ret);
	system("pause");
	return 0;
}

Mystrstr

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
char* Mystrstr(const char* str1, const char* str2)
{
	assert(str1 && str2);
	const char* s1 = str1;
	const char* s2 = str2;
	const char* cur = str1;

	if (str2 == '\0')
		return (char*)str1;
	while (*cur)
	{
		s1 = cur;
		s2 = str2;
		//chazhao
		while (*s1 == *s2 && *s1 && *s2)
		{
			s1++;
			s2++;
		}
		if (*s2 == '\0')
		{
			return (char*)cur;
		}
		cur++;
	}
	return NULL;
}
int main()
{
	char str1[] = "abbbcgygy";
	char* str2 = "bbc";
	char* ret = Mystrstr(str1, str2);
	printf("%s\n", ret);
	system("pause");
	return 0;
}

不能理解的话，可以像上图一样用画图的方式演示一遍，这样就会很快理解。