c strcpy strncpy

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <string.h>
using namespace std;

int main()
{
const char* p = "hello world";
char des[128];
//memset(des, 0x00, sizeof(des));
/*
Warning: If there is no null byte among the first n bytes of src, the string placed in dest will  not  be
null-terminated.
*/
strncpy(des, p, 7);//不包含最后的null-terminated.
cout << des << endl;//打印出乱码
return 0;
}

#define _CRT_SECURE_NO_WARNINGS

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

int main()
{
char *src = "123 hello world";
char des[6] = { 0, };
//strncpy(des, src, strlen(src));//奔溃
strncpy(des, src, sizeof(des) - 1);//最多拷贝des的长度-1，最后一个放置 '\0'
printf("%s\n",des);
}

//讨论优先级 * 和++ 是同一优先级但是，后加加时执行完语句后执行++操作
char* strcpy(char* des,const char* source)
{
　
 char* r=des;
   
  assert((des != NULL) && (source != NULL));
 
　while((*r++ = *source++)!='\0');
 
　return des;
　
}