程序崩溃时释放字符数组 [英] Programme crashes while deallocating a character array

问题描述

当我运行的.exe是用调试模式下面的代码创建的，它显示一些断言失败和程序崩溃但是当我运行相同的exe创建从下面的代码的发布模式，其工作正常。 / p>

请帮助确定为什么我在调试模式下取消断言失败，而不是在释放模式下。

 ＃include< iostream> 
 using namespace std; 
＃include< string.h> 
 
 void main（）
 {
 char * buf = new char [5]; //预分配缓冲区
 buf =Hello; 
 delete [] buf; 
 getchar（）; 
 // cout<< buf; 
 // string * p = new（buf）string（hi）; // placement new 
 // string * q = new string（hi）; //普通堆分配
} 
  

解决方案

p> char * buf = new char [5]; //预分配缓冲区


这里你定义一个指针，并初始化它指向一个动态分配

  buf =Hello; 
  

这里你初始化指针指向字符串文字的开头。

  delete [] buf; 
 

这里你删除[] buf指针，但是buf指针不再指向任何你新的[ ]'d，它指向字符串字面量。你只能删除/删除[]一个指针，指向你从新的/新的[]。所以你得到未定义的行为，可能会崩溃

你可能想把你的字符串的内容复制到你的新缓冲区[]'d。请记住nul终结符的帐户：

  int main（）
 {
 char * buf = new char [6]; // pre-allocated buffer 
 strcpy（buf，Hello）; 
 delete [] buf; 
 getchar（）; 
 // cout<< buf; 
 // string * p = new（buf）string（hi）; // placement new 
 // string * q = new string（hi）; //普通堆分配
} 
  

然而，在C ++中， :: string from #include< string> ;

  std： ：string =Hello; 
  

When I run the .exe being created with the below code in debug mode , it shows some assertion failure and the programme crashes But when i run the same exe created from the release mode of the below code , its working fine.

Please help to identify why I am geting the assertion failure in debug mode but not in release mode .

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

void main()
{
    char *buf  = new char[5];   //pre-allocated buffer
    buf = "Hello";
    delete [] buf;
    getchar();
    //cout<<buf;
    //string *p = new (buf) string("hi");  //placement new
    //string *q = new string("hi");  //ordinary heap allocation
}

解决方案

 char *buf  = new char[5];   //pre-allocated buffer

Here you define a pointer, and initialize it to point to a dynamically allocated buffer with room for 5 characters.

buf = "Hello";

Here you initialize the pointer to point to the beginning of a string literal.

 delete [] buf;

Here you delete[] the buf pointer, but the buf pointer no longer points to anything you new[]'d up, it points to the string literal. You can only delete/delete[] a pointer that points to something you got from new/new[]. So you get undefined behavior, and likely crash

You likely meant to copy the content of your string into the buffer you new[]'d. Remember to account for the nul terminator:

int main()
{
    char *buf  = new char[6];   //pre-allocated buffer
    strcpy(buf, "Hello");
    delete [] buf;
    getchar();
    //cout<<buf;
    //string *p = new (buf) string("hi");  //placement new
    //string *q = new string("hi");  //ordinary heap allocation
}

Though, in C++, you'd rather use std::string from #include <string>;

std::string = "Hello";

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