【C】库函数之strncpy

Copy characters from string

# include <string.h>
char * strncpy(char * dest, const char * src, int count);

Copies the first num characters of source to destination. If the end of the source C string (which is signaled by a null-character) is found before num characters have been copied, destination is padded with zeros until a total of num characters have been written to it.

上述内容是C++官网对strncpy函数的介绍，可以看出与strcpy函数不同的是，src指向的C字符串复制到dest所指向的数组中，复制的字符长度为count。如果src指向的字符串长度小于count，那么在dest指向的字符串后面追加'\0'，直到满足本次复制的字符长度为count。(ps:strcpy函数实现)

接下来给出实现strncpy函数的源代码：

#define _CRT_SECURE_NO_WARNINGS 1

/*
* Copyright (c) 2018, code farmer from sust
* All rights reserved.
*
* 文件名称：MyStrncpy.c
* 功能：实现库函数strncpy
*       char * strncpy (char * destination, const char * source, int count)
*
* 当前版本：V1.0
* 作者：sustzc
* 完成日期：2018年5月6日17:06:53
*/

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

/*
*	函数名称：MyStrncpy
*
*	函数功能：复制源字符串的内容
*             将src指向的C字符串复制到dest所指向的数组中，复制的字符长度为count。
*             如果src指向的字符串长度小于count，那么在dest指向的字符串后面追加'\0'，
*             直到满足本次复制的字符长度为count
*
*	入口参数：dest, src, count
*
*	出口参数：dest
*
*	返回类型：char *
*/

char * MyStrncpy(char * dest, const char * src, int count)
{
	char * cp = dest;

	assert((NULL != src) && (NULL != cp));
		
	while (count && (*cp++ = *src++))
	{
		count--;
	}

	if (count)
	{
		while (--count)
		{
			*cp++ = '\0';
		}
	}
	else
	{
		;
	}

	return dest;
}

int main(void)
{
	char str1[10] = "abcde";
	char str2[5] = "1234";

	printf("str1: %s\n", str1);
	printf("str2: %s\n", str2);
	printf("copy after,str1: %s\n", MyStrncpy(str1, str2, 5));

	return 0;
}

输出结果

【C】库函数之strncpy

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