字符串函数---strcpy() strcnpy()

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
/**
 *date: 2019.6.11
 *描述:要求用户输入以q开头的单词，该程序把输入拷贝到一个临时数组中，如果第一个字母是q,程序调用strcpy()把 
 *整个字符串从临时数组中拷贝至目标数组中 
 */ 
#define SIZE 40
#define LIM 5
char* s_gets(char* st, int n);
int main(int argc, char *argv[]) {
	
	char qwords[LIM][SIZE];
	char temp[SIZE];
	int i = 0;
	
	printf("Enter %d words beginning with q:
", LIM);
	while (i < LIM && s_gets(temp, SIZE))
	{
		if(temp[0] != q)
		{
			printf("%s doesnt begin with q
", temp);
		}
		else
		{
			strcpy(qwords[i],temp);
			i++;
		}
	}
	puts("Here are the words accepted:");
	for ( i = 0; i < LIM; i++)
	{
		puts(qwords[i]);
	}	
	return 0;
}

char* s_gets(char* st, int n)
{
	char* ret_val;
	int i = 0;
	
	ret_val = fgets(st, n, stdin);
	if(ret_val)
	{
		while (st[i] != 
 && st[i] != )
		{
			i++;
		}
		if (st[i] == 
)
		{
			st[i] = ;
		}
		else
		{
			while (getchar() != 
)
				continue;
		}		
	}
	return ret_val;
	
}

运行结果:

Enter 5 words beginning with q:
quit
quiet
quick
quiz
test
test doesnt begin with q
quote
Here are the words accepted:
quit
quiet
quick
quiz
quote

下面写一个小的测试程序来对比一下strcpy与strncpy

1.strcpy()

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

int main(int argc, char *argv[]) {
	char test1[] = "helloworld";
	char test2[] = "aaaaaa";
	printf("test1:0x%x,test2:0x%x
",test1,test2);
	printf("strlen(test1):%d,strlen(test2):%d
",strlen(test1),strlen(test2));
	strcpy(test2,test1);
	//strncpy(test2,test1,strlen(test2) - 1);
	//test2[strlen(test2) - 1] = ;

	puts(test1);
	puts(test2);
		
	return 0;
}

运行结果:

test1:0x62fe30,test2:0x62fe20
strlen(test1):10,strlen(test2):6
helloworld
helloworld

从该程序中可以看到，若目标字符串的空间小于源字符串的空间，使用strcpy，会导致缓冲区溢出。

test2[]的大小为6，但是在调用strcpy后，输出的字符串大小为10，很明显，占用了别的内存空间。

2.strncpy

strncpy()与strcpy()的不同之处在于：它会检查目标空间是否能够容纳原字符串的副本。该函数的第三个参数指明可拷贝的最大字符数。

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

int main(int argc, char *argv[]) {
	char test1[] = "helloworld";
	char test2[] = "aaaaaa";
	printf("test1:0x%x,test2:0x%x
",test1,test2);
	printf("strlen(test1):%d,strlen(test2):%d
",strlen(test1),strlen(test2));
	//strcpy(test2,test1);
	strncpy(test2,test1,strlen(test2) - 1);
	test2[strlen(test2) - 1] = ;

	puts(test1);
	puts(test2);
		
	return 0;
}

运行结果:

test1:0x62fe30,test2:0x62fe20
strlen(test1):10,strlen(test2):6
helloworld
hello