strncpy和strcat不工作，我认为他们会c ++ [英] strncpy and strcat not working the way I think they would c++

问题描述

我有一个任务来自己实现一个字符串对象，并且当试图连接两个这样的字符串时，它现在被卡住了。我想我会走这条路：

• 分配足够大的空间来容纳


• 使用strncpy将字符串保存到新空间中（本部分工作原理）


• 在字符串上的猫我插入


• 持有字符串

执行：

  #include< iostream> 
 #include< cstring> 
 
使用namespace std; 
 
 int main（）{
 int index = 6; //插入位置
 
 char * temp = new char [21]; 
 char * mystr = new char [21 + 7 +1]; 
 char * insert = new char [7]; 
 
 temp =你好，这是一个测试; 
 insert =world; 
 
 strncpy（mystr，temp，index）; 
 strcat（mystr + 7，insert）; 
 strcat（mystr，temp + index）; 
 mystr [21 + 6] ='\0'; 
 
 cout<< mystr：<< mystr<< ENDL; 
 
返回0; 
} 
  

代码在使用可视化工作室时在Hello之后打印乱码，但在使用g ++（有警告），为什么差异？

解决方案

您将c本机概念与c ++混合使用。不是一个好主意。

这更好：

  #include <&的iostream GT; 
 #include< string> //不是cstring 
 
 using namespace std; 
 
 int main（）{
 int index = 6; //插入位置
 
字符串temp =你好，这是一个测试; 
 string insert =world; 
 string mystr = temp.substr（0，index）+ insert + temp.substr（index）; 
 
 cout<< mystr：<< mystr<< ENDL; 
 
返回0; 
} 
  

I have an assignment to implement a string object ourselves, and am currently stuck when trying to concatenate two such strings. I figured I would go this route:

• allocate big enough space to hold
• insert beginning of holding string into new space up to index using strncpy(this part works)
• cat on the string I am inserting
• cat on the remainder of the holding string

Implementation:

#include <iostream>
#include <cstring>

using namespace std;

int main(){
   int index = 6;//insertion position

   char * temp = new char[21];
   char * mystr = new char[21 + 7 +1];
   char * insert = new char[7];

   temp = "Hello this is a test";
   insert = " world ";

   strncpy(mystr, temp, index); 
   strcat(mystr + 7, insert);     
   strcat(mystr, temp + index);
   mystr[21 + 6] = '\0'; 

   cout << "mystr: " << mystr << endl;

   return 0;
}

that code prints out gibberish after Hello when using visual studios, but works when using g++ (with warnings), why the discrepancy?

解决方案

You're mixing native c concepts with c++. Not a good idea.

This is better:

#include <iostream>
#include <string>  // not cstring

using namespace std;

int main(){
   int index = 6;//insertion position

   string temp = "Hello this is a test";
   string insert = "world ";
   string mystr = temp.substr(0, index) + insert + temp.substr(index);

   cout << "mystr: " << mystr << endl;

   return 0;
}

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