qt QFlags：有符号值超出枚举常量的范围

Question

I got following warnings for the enum value xxxxx920P4 building a qt C++ project. And I found out in the debugging that xxxxx920P4 is now equals to xxxxxundefine ( 0x00000000 ), which causes the unexpected result. How should I resolve this problem?

I'm using Qt version: 4.8.7 and Visual studio 2010.

The following loop will not be executed. gVersions[0].verNum is "xxxxx920P4" , so I guess "xxxxx920P4" 's value has been truncated and now it equals to 0x00000000 .

for(int i=0; gVersions[i].verNum != xxxxxundefine ; i++)
{
}

Doc for Qt Qflags class: https://doc.qt.io/qt-5/qflags.html

warning C4341: 'xxxxx920P4' : signed value is out of range for enum constant
    
warning C4309: 'initializing' : truncation of constant value

enum Version
{
    xxxxxundefine   = 0x00000000,
    xxxxx400     = 0x00000001,
    xxxxx401     = 0x00000002,
    xxxxx410     = 0x00000004,
    xxxxx411     = 0x00000008,
    xxxxx412     = 0x00000010,
    xxxxx420     = 0x00000020,
    xxxxx430     = 0x00000040,
    xxxxx431     = 0x00000080,
    xxxxx432     = 0x00000100,
    xxxxx440     = 0x00000200,
    xxxxx500     = 0x00000400,
    xxxxx510     = 0x00000800,
    xxxxx520     = 0x00001000,
    xxxxx521     = 0x00002000,
    xxxxx600     = 0x00004000,
    xxxxx611     = 0x00008000,
    xxxxx620     = 0x00010000,
    xxxxx621     = 0x00020000,
    xxxxx700     = 0x00040000,
    xxxxx910     = 0x00080000,
    xxxxx910P5   = 0x00100000,
    xxxxx910P6   = 0x00200000,
    xxxxx910P11  = 0x00400000,
    xxxxx910P12  = 0x00800000,
    xxxxx910P13  = 0x01000000,
    xxxxx910P14  = 0x02000000,
    xxxxx910P15  = 0x04000000,
    xxxxx910P16  = 0x08000000,
    xxxxx920     = 0x10000000,
    xxxxx920P1   = 0x20000000,
    xxxxx920P2   = 0x40000000,
    xxxxx920P3   = 0x80000000,
    xxxxx920P4   = 0x100000000,
}; Q_DECLARE_FLAGS(Versions, Version)

Answer 1

The last value is too long to fit into aa non-long int. While newer compilers may try to choose a larger integral type for it, some older ones would complain. GCC tends to do the former unless you choose type explicitly. Note that second to last value 0x80000000 or any combination of masks involving it would not fit into int , it's essentially a negative -2147483648.

 enum Version : long long  
 {
     //...
     xxxxx920P4   = 0x100000000,
 }; 

PS. Apparently Qt5 doesn't support something different from ( unsigned ) int : https://doc.qt.io/qt-5/qflags.html