C++ new的nothrow关键字和new_handler用法

C++ new的nothrow关键字和new_handler用法

new && new(std::nothrow)

new(std::nothrow) 顾名思义，即不抛出异常，当new一个对象失败时，默认设置该对象为NULL，这样可以方便的通过if(p == NULL) 来判断new操作是否成功

普通的new操作，如果分配内存失败则会抛出异常，虽然后面一般也会写上if(p == NULL) 但是实际上是自欺欺人，因为如果分配成功，p肯定不为NULL；而如果分配失败，则程序会抛出异常，if语句根本执行不到。

因此，建议在c++代码中，凡是涉及到new操作，都采用new(std::nothrow)，然后if(p==NULL)的方式进行判断

#include <new>
#include <iostream>
#include <stdlib.h>
#include <stdio.h>

using namespace std;

//void __cdecl newhandler()
//{
//  printf(".....%20s,%10d,,,,,,,\n", __FUNCTION__, __LINE__);
//  return;
//}

int main()
{
//  set_new_handler(newhandler);

    char *p = new char[0x2000000];
    if(NULL == p)
    {
        //记录日志
        printf(".....%20s,%10d,,,,,,,\n", __FUNCTION__, __LINE__);
        return false;
    }
    printf(".....%20s,%10d, p=0x%10x,,,,,,,\n", __FUNCTION__, __LINE__, p); 

    return 0;
}

不做任何处理，抛出异常：

[[email protected] nfs] # ./a.out
terminate calleda.out/636: potentially unexpected fatal signal 6.
 after throwing
an instance of ‘
Pid: 636, comm:                a.out

  what():  std:CPU: 0    Tainted: P             (3.0.8 #1-svn16375)
:bad_alloc
PC is at 0x40253a98
LR is at 0x40253a44
pc : [<40253a98>]    lr : [<40253a44>]    psr: 60000010
sp : bef34bb0  ip : 4029615c  fp : bef34c6c
r10: 008ae1d8  r9 : 00000000  r8 : 401ca704
r7 : 0000010c  r6 : 40296394  r5 : 00000006  r4 : 0000027c
r3 : 40296144  r2 : 00000006  r1 : 0000027c  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode USER_32  ISA ARM  Segment user
Control: 0005317f  Table: 824bc000  DAC: 00000015
[<c002dd4c>] (show_regs+0x0/0x50) from [<c0055e08>] (get_signal_to_deliver+0x35c/0x384)
 r4:020c0027 r3:0000000a
[<c0055aac>] (get_signal_to_deliver+0x0/0x384) from [<c002eb70>] (do_signal+0x70/0x56c)
[<c002eb00>] (do_signal+0x0/0x56c) from [<c002f0c0>] (do_notify_resume+0x54/0x60)
[<c002f06c>] (do_notify_resume+0x0/0x60) from [<c002c194>] (work_pending+0x24/0x28)
 r4:0000027c r3:20000013
Aborted

若设置了set_new_handler，则会进入到死循环