测试strncpy与strcpy，strlen 与sizeof的区别

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#strncpy与strcpy #strlen 与sizeof

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本文通过实例演示了strcpy与strncpy函数的使用方法，并对比了它们的行为差异。同时介绍了strlen与sizeof的不同之处。

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测试strncpy与strcpy，

strlen 与sizeof的区别

strlen(str)，从头开始计数，遇到'\0'结束，sizeof 只与定义有关

常考题

#include <stdio.h>
#include <string.h>

void main()
{
	/*
	*	第一部分测试strcpy
	*/
	char str[10]="ABCDEFGHI";
	printf("before use strcpy  the str is %s and strlen is %d sizeof(str)=%d\n",str,strlen(str),sizeof(str));
	//复制字符串到str，从起始位置开始，复制完成后末尾添加'\0'	
	strcpy(str,"CCCC");
	printf("after use strcpy   the str is %s and strlen is %d sizeof(str)=%d\n",str,strlen(str),sizeof(str));
	int i=0;	
	for(i=0;i<10;i++)
	{
		printf("str[%d] is %c\n",i,str[i]);
	}
	strcpy(str,"BBB");
	printf("after use strcpy   the str is %s and strlen is %d sizeof(str)=%d\n",str,strlen(str),sizeof(str));
	strcpy(str,"A");
	printf("after use strcpy   the str is %s and strlen is %d sizeof(str)=%d\n\n\n",str,strlen(str),sizeof(str));
	
	/*
	*	第二部分测试strncpy
	*/	
	char str1[10]="ABCDEFGHI";
	printf("before use strncpy the str is %s and is %d sizeof(str)=%d\n",str1,strlen(str1),sizeof(str1));
	//复制字符串到str1，从起始位置开始，指定复制的长度，不足的长度字符串补充'\0'
	strncpy(str1,"CCC",5);
	printf("after use strncpy  the str is %s and is %d sizeof(str)=%d\n",str1,strlen(str1),sizeof(str1));
	for(i=0;i<10;i++)
	{
		printf("str1[%d] is %c\n",i,str1[i]);
	}

	strncpy(str1,"BB",2);
	printf("after use strncpy  the str is %s and is %d sizeof(str)=%d\n",str1,strlen(str1),sizeof(str1));
	strncpy(str1,"A",1);
	printf("after use strncpy  the str is %s and is %d sizeof(str)=%d\n",str1,strlen(str1),sizeof(str1));
}

结果如下：

before use strcpy  the str is ABCDEFGHI and strlen is 9 sizeof(str)=10
after use strcpy   the str is CCCC and strlen is 4 sizeof(str)=10
str[0] is C
str[1] is C
str[2] is C
str[3] is C
str[4] is 
str[5] is F
str[6] is G
str[7] is H
str[8] is I
str[9] is 
after use strcpy   the str is BBB and strlen is 3 sizeof(str)=10
after use strcpy   the str is A and strlen is 1 sizeof(str)=10


before use strncpy the str is ABCDEFGHI and is 9 sizeof(str)=10
after use strncpy  the str is CCC and is 3 sizeof(str)=10
str1[0] is C
str1[1] is C
str1[2] is C
str1[3] is 
str1[4] is 
str1[5] is F
str1[6] is G
str1[7] is H
str1[8] is I
str1[9] is 
after use strncpy  the str is BBC and is 3 sizeof(str)=10
after use strncpy  the str is ABC and is 3 sizeof(str)=10