new、delete、指向连续空间的指针、数组、空间释放、空间申请

1. 使用 new 得来的空间，必须用 delete 来释放；使用 new [] 得来的空间，必须用 delete [] 来释放。彼此之间不能混用。用 new [] 分配出连续空间后，指针变量“指向”该空间的首地址。

2. 指针通过 new 或 new[] ，向系统“申请”得到一段内存空间，这段内存空间必须在不需要将它释放了。

3. 一个指针被删除时，应指向最初的地址

4.  已释放的空间，不可重复释放



1, 2 的使用错误例子

int* p = new int[100];

int girl[100];

p = girl;

delete [] p;

错误一： 该释放的new int[100] 没有使用
错误二： girl[1]00]本应由系统自行释放，但我们要强行释放
主意P的指向发生了变化

3的错误使用例子

int main(){

int* p = new int[3];

*p=1;

p++; 

*p = 2;

delete []p; //P的位置不是指向初始位置
}


==15033== Invalid free() / delete / delete[]
==15033==    at 0x4A056AF: operator delete[](void*) (vg_replace_malloc.c:368)
==15033==    by 0x40061E: main (test3.cpp:15)
==15033==  Address 0x512e044 is 4 bytes inside a block of size 12 alloc'd
==15033==    at 0x4A065BA: operator new[](unsigned long) (vg_replace_malloc.c:264)
==15033==    by 0x4005E9: main (test3.cpp:3)
==15033== 
==15033== 
==15033== HEAP SUMMARY:
==15033==     in use at exit: 12 bytes in 1 blocks
==15033==   total heap usage: 1 allocs, 1 frees, 12 bytes allocated
==15033== 
==15033== 12 bytes in 1 blocks are definitely lost in loss record 1 of 1
==15033==    at 0x4A065BA: operator new[](unsigned long) (vg_replace_malloc.c:264)
==15033==    by 0x4005E9: main (test3.cpp:3)
==15033== 
==15033== LEAK SUMMARY:
==15033==    definitely lost: 12 bytes in 1 blocks
==15033==    indirectly lost: 0 bytes in 0 blocks
==15033==      possibly lost: 0 bytes in 0 blocks
==15033==    still reachable: 0 bytes in 0 blocks
==15033==         suppressed: 0 bytes in 0 blocks
==15033== 
==15033== For counts of detected and suppressed errors, rerun with: -v
==15033== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 4 from 4)

正确的释放
当我们的指针指向变化很多次时，在释放前要保证一步不错地一一退回，会比较困难。所以另一方法是在最初时“备份”一份。在释放时，直接释放该指针即可。

int main(){

int* p = new int[3];

int* pbak;

pbak=p;

*p=1;

p++; 

*p = 2;

delete [] pbak;
}