t1.cpp //C++
//.....................
int main()
{
int* p;
int* p1;
p1=new (std::nothrow)int[-1]; //失败后返回NULL
if(p1==NULL)
{
printf("\r\n p1 error....");
}
p = new int[-1]; //失败后抛出异常
if(p==NULL) //当失败后实际上执行不到这.
{
printf("\r\n p error....");
}
return(0);
}
gridserver1:/share/suse linux/root/c # g++ -g t1.cpp
gridserver1:/share/suse linux/root/c # gdb a.out
This GDB was configured as "x86_64-suse-linux"...
Using host libthread_db library "/lib64/libthread_db.so.1".
(gdb) b main
Breakpoint 1 at 0x40083c: file t1.cpp, line 10.
(gdb) disass main //如下看到,实际上编译器把c/c++源代码中的不同new的用法处理成了不同的调用.
Dump of assembler code for function main:
0x0000000000400834
: push %rbp
0x0000000000400835 : mov %rsp,%rbp
0x0000000000400838 : sub $0x10,%rsp
0x000000000040083c : mov $0x500d50,%esi
0x0000000000400841 : mov $0xfffffffffffffffc,%rdi
0x0000000000400848 : callq 0x4006d8 <_ZnamRKSt9nothrow_t@plt> //失败直接返回NULL的new
0x000000000040084d : mov %rax,0xfffffffffffffff8(%rbp)
0x0000000000400851 : cmpq $0x0,0xfffffffffffffff8(%rbp)
0x0000000000400856 : jne 0x400867
0x0000000000400858 : mov $0x400988,%edi
0x000000000040085d : mov $0x0,%eax
0x0000000000400862 : callq 0x4006c8
0x0000000000400867 : mov $0xfffffffffffffffc,%rdi
0x000000000040086e : callq 0x4006b8 <_Znam@plt> //失败抛出异常的new
0x0000000000400873 : mov %rax,0xfffffffffffffff0(%rbp)
0x0000000000400877 : cmpq $0x0,0xfffffffffffffff0(%rbp)
0x000000000040087c : jne 0x40088d
0x000000000040087e : mov $0x400998,%edi
0x0000000000400883 : mov $0x0,%eax
0x0000000000400888 : callq 0x4006c8
0x000000000040088d : mov $0x0,%eax
0x0000000000400892 : leaveq
0x0000000000400893 : retq
End of assembler dump.
(gdb) n
The program is not being run.
(gdb) r
Starting program: /share/suse linux/root/c/a.out
Breakpoint 1, main () at t1.cpp:10
10 p1=new (std::nothrow)int[-1];
(gdb) n
11 if(p1==NULL)
(gdb) n
13 printf("\r\n p1 error....");
(gdb) n
16 p = new int[-1];
(gdb) n
terminate called after throwing an instance of 'std::bad_alloc'
what(): St9bad_alloc
p1 error....
Program received signal SIGABRT, Aborted.
0x00002b591b4bcbb5 in raise () from /lib64/libc.so.6
(gdb)
t2.cpp //c++
int main()
{
int* p;
int* p1;
p1=new (std::nothrow)int[-1];
if(p1==NULL)
{
printf("\r\n p1 error....");
}
try{
p = new int[-1];
}catch(const std::bad_alloc&e){
printf("\r\n p error............");
}
return(0);
}
gridserver1:/share/suse linux/root/c # g++ -g t2.cpp
gridserver1:/share/suse linux/root/c # gdb a.out
This GDB was configured as "x86_64-suse-linux"...
Using host libthread_db library "/lib64/libthread_db.so.1".
(gdb) disass main
Dump of assembler code for function main:
0x00000000004009a4 : push %rbp
0x00000000004009a5 : mov %rsp,%rbp
0x00000000004009a8 : push %rbx
0x00000000004009a9 : sub $0x28,%rsp
0x00000000004009ad : mov $0x500f58,%esi
0x00000000004009b2 : mov $0xfffffffffffffffc,%rdi
0x00000000004009b9 : callq 0x400838 <_ZnamRKSt9nothrow_t@plt> //new
0x00000000004009be : mov %rax,0xffffffffffffffe8(%rbp)
0x00000000004009c2 : cmpq $0x0,0xffffffffffffffe8(%rbp)
0x00000000004009c7 : jne 0x4009d8
0x00000000004009c9 : mov $0x400b38,%edi
0x00000000004009ce : mov $0x0,%eax
0x00000000004009d3 : callq 0x400818
0x00000000004009d8 : mov $0xfffffffffffffffc,%rdi
0x00000000004009df : callq 0x400808 <_Znam@plt>
0x00000000004009e4 : mov %rax,0xffffffffffffffe0(%rbp)
0x00000000004009e8 : jmp 0x400a3a
0x00000000004009ea : mov %rax,0xffffffffffffffd0(%rbp)
0x00000000004009ee : cmp $0x1,%rdx
0x00000000004009f2 : je 0x4009fd
0x00000000004009f4 : mov 0xffffffffffffffd0(%rbp),%rdi
0x00000000004009f8 : callq 0x400848 <_Unwind_Resume@plt>
0x00000000004009fd : mov 0xffffffffffffffd0(%rbp),%rdi
0x0000000000400a01 : callq 0x400828 <__cxa_begin_catch@plt>
0x0000000000400a06 : mov %rax,0xfffffffffffffff0(%rbp)
0x0000000000400a0a : mov $0x400b48,%edi
0x0000000000400a0f : mov $0x0,%eax
0x0000000000400a14 : callq 0x400818
0x0000000000400a19 : callq 0x4007d8 <__cxa_end_catch@plt>
0x0000000000400a1e : jmp 0x400a3a
0x0000000000400a20 : mov %rax,0xffffffffffffffd0(%rbp)
0x0000000000400a24 : mov 0xffffffffffffffd0(%rbp),%rbx
0x0000000000400a28 : callq 0x4007d8 <__cxa_end_catch@plt>
0x0000000000400a2d : mov %rbx,0xffffffffffffffd0(%rbp)
0x0000000000400a31 : mov 0xffffffffffffffd0(%rbp),%rdi
0x0000000000400a35 : callq 0x400848 <_Unwind_Resume@plt>
0x0000000000400a3a : mov $0x0,%eax
0x0000000000400a3f : add $0x28,%rsp
0x0000000000400a43 : pop %rbx
0x0000000000400a44 : leaveq
0x0000000000400a45 : retq
End of assembler dump.
(gdb) b main
Breakpoint 1 at 0x4009ad: file t2.cpp, line 10.
(gdb) n
The program is not being run.
(gdb) r
Starting program: /share/suse linux/root/c/a.out
Breakpoint 1, main () at t2.cpp:10
10 p1=new (std::nothrow)int[-1];
(gdb) n
11 if(p1==NULL)
(gdb) n
13 printf("\r\n p1 error....");
(gdb) n
16 p = new int[-1];
(gdb) n
p1 error....
p error............
Program exited normally.
(gdb)
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