[英]c++ delete [] always hangs
I have implemented my own simple vector, all functions seems fine except on alloc_new()
, when it tries to create new memory and copy the contents their and delete the old memory allocation. 我已经实现了自己的简单向量,当尝试创建新内存并复制其内容并删除旧的内存分配时,除了alloc_new()
之外,所有功能似乎都不错。 My programs always hangs and never execute after that. 我的程序总是挂起,此后再也不执行。
class myvector{
private:
int vsize, maxsize;
int* arr;
void alloc_new();
public:
myvector();
myvector(int);
myvector(const myvector&);
~myvector();
void push_back(int);
int size();
int operator[](int);
int at(int);
void display();
};
myvector::myvector(){
maxsize = 20;
vsize = 0;
arr = new int[maxsize];
}
void myvector::alloc_new(){
// Allocate new space, double of current size
maxsize = maxsize*2;
int* arr_new = new int[maxsize];
//copy the elements from the base location to new location
for(int i=0; i < vsize ; i++)
arr_new[i] = arr[i];
delete[] arr; // MY PROGRAM ALWAYS HANGS HERE
arr = arr_new;
}
void myvector::push_back(int val){
if((vsize+1) > maxsize)
alloc_new();
arr[++vsize] = val;
}
int main(){
myvector vect;
for(int i=0;i<25;i++){
vect.push_back(rand()%100+1);
}
getch();
}
The problem is that your "have we reached max size" is wrong. 问题是您的“达到最大尺寸”是错误的。 You are comparing vsize + 1 > maxsize
. 您正在比较vsize + 1 > maxsize
。 This means that you are writing to arr[++vsize]
when vsize + 1 == maxsize
. 这意味着当vsize + 1 == maxsize
时,您正在写arr[++vsize]
。 This writes one element PAST your allocation [in other words, index 20 were 0..19 are valid indices], and thus goes wrong. 这将为您的分配写入一个元素PAST [换句话说,索引20为0..19是有效索引],因此出错。
Fix the code like this: 像这样修复代码:
void myvector::push_back(int val){
if((vsize+1) >= maxsize)
alloc_new();
arr[++vsize] = val;
}
Using valgrind will tell you: 使用valgrind将告诉您:
$ valgrind ./a.out
==20918== Memcheck, a memory error detector
==20918== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==20918== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==20918== Command: ./a.out
==20918==
==20918== Invalid write of size 4
==20918== at 0x4009E9: myvector::push_back(int) (in /home/MatsP/src/junk/a.out)
==20918== by 0x400AA1: main (in /home/MatsP/src/junk/a.out)
==20918== Address 0x5a20090 is 0 bytes after a block of size 80 alloc'd
==20918== at 0x4C2A77C: operator new[](unsigned long) (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==20918== by 0x4008B4: myvector::myvector() (in /home/MatsP/src/junk/a.out)
==20918== by 0x400A57: main (in /home/MatsP/src/junk/a.out)
==20918==
==20918==
==20918== HEAP SUMMARY:
==20918== in use at exit: 0 bytes in 0 blocks
==20918== total heap usage: 2 allocs, 2 frees, 240 bytes allocated
==20918==
==20918== All heap blocks were freed -- no leaks are possible
==20918==
==20918== For counts of detected and suppressed errors, rerun with: -v
==20918== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
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