The system is Windows 10 x64, MinGW has been installed, the version is:
mingw32-gcc 5.3.0-3
mingw32-gcc-g++ 5.3.0-3
mingw32-gdb 7.6.1- 1
Now I try to compile and debug a cpp code test1.cpp:

#include <iostream>
using namespace std;
int main()
{
    int a;
    cout<<"HelloWorld!"<<endl;
    cin>>a;
}

Then compile using g++:

g++ -g test1.cpp -o test1.exe

Pass, get test1.exe, and then use gdb to debug:

gdb test1.exe
Getting error:
GNU gdb (GDB) 7.6.1
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law . Type "show copying"
and "show warranty" for details.
This GDB was configured as "mingw32".
For bug reporting instructions, please see:
http://www.gnu .org/software/g......
"D:\CppProjects/test1.exe": not in executable format: File format not recognized
(gdb)

How to solve it?