strcpy_s：拷贝整个字符串

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

int main()
{
	char str1[] = "first stringiiii";
	char str2[] = "second string";
	char str3[100];

	strcpy_s(str1, sizeof(str1) / sizeof(str1[0]), str2);
	strcpy_s(str3, sizeof(str3) / sizeof(str3[0]), "copy end");

	//strcpy(str1, str2);
	//strcpy(str3, "copy end");

	printf("str1：%s\n", str1);
	printf("str2：%s\n", str2);
	printf("str3：%s\n", str3);

	system("pause");

	return 0;
}

str1：second string
str2：second string
str3：copy end
请按任意键继续. . .

注意：str2比str1长度一定要小，不然会报错。

strncpy_s：拷贝字符串的前n个字符

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

int main()
{
	char str1[] = "to be or not to be";
	char str2[40];
	strncpy_s(str2, sizeof(str2), str1, 5);
	str2[5] = '\0';

	printf("str2:%s\n", str2);
	system("pause");

	return 0;
}

str2:to be
请按任意键继续. . .

strcat_s 字符串连接

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

int main()
{
	char str1[] = "I love ";
	char str2[] = "apple";

	int len = strlen(str1) + strlen(str2) +1;

	
	strcat_s(str1, len, str2);

	printf("str1:%s\n", str1);
	
	system("pause");

	return 0;
}

str1:I love apple
请按任意键继续. . .

strncat_s：连接指定数量的字符串

strcmp：比较整个字符串

strncmp：比较字符串前n个字符