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最新推荐文章于 2025-04-02 22:49:43 发布

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#strncpy #strncat #strncmp

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本文详细介绍了如何使用C语言模拟实现三个常见的字符串操作函数：strncpy、strncat和strncmp。通过源代码示例，读者可以深入理解这些函数的工作原理，并学习到如何在实际编程中正确地使用它们。

1.模拟实现strncpy

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<assert.h>

char* my_strncpy(char *dest, const char *src, size_t num)
{
	char *ret = dest;
	assert(dest != NULL);
	assert(src != NULL);

	while(num--)
	{
		if( ! (*dest++ = *src++))
		{
			return ret;
		}
	}
	*dest = '\0';

	return ret;
}

int main()
{
	char arr1[8] = "abcdefg";
	char arr2[1024] = {0};
	my_strncpy(arr2, arr1, 3);
	//strncpy(arr2, arr1, 10);
	printf("%s\n",arr2);

	return 0;
}

2.模拟实现strncat


#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include<assert.h>
#include <string.h>

char *my_strncat(char *dest, const char *src, size_t num)
{
	char *ret = dest;
	assert(dest != NULL);
	assert(src != NULL);

	while(*dest)
	{
		dest++;
	}
	while(num--)
	{
		if( ! (*dest++ = *src++))
			return ret;
	}
	*dest = '\0';

	return ret;
}

int main()
{
	char a[30] = "tomorrow";
	my_strncat(a," better!", 3);
	printf("%s\n",a);
	return 0;
}

3.实现strncmp


#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int my_strncmp(const char *str1, const char *str2, size_t num)
{
	while(*str2 && *str1 && --num)
	{
		if(*str1 == *str2)
		{
			str1++;
		    str2++;
		}
		else
			break;
	}
	if((unsigned char)*str1 > (unsigned char)*str2)
		return 1;
	else if((unsigned char)*str1 < (unsigned char)*str2)
		return -1;
	return 0;
}

int main()
{
	char str1[10] = "abcd";
	printf("%d\n",my_strncmp(str1, "abcde", 3));
	printf("%d\n",my_strncmp(str1, "abcef",4));
	printf("%d\n",my_strncmp(str1, "aac", 2));
	return 0;
}