Question

这是我检查笔记本电脑电池状态的代码。我没有做到这一点，因为编译器给我一个关于switch案例的错误：

UPower *u = new UPower(this);

    Battery *b;
    foreach (Battery *bat, *u->batteries()) {
        b = u->batteries()->value(bat->path());
    }
    ui->batteryProg->setValue(b->percentage());

    switch( b->state() ) {
        case Battery::FullyCharged:
            ui->batteryStatus->setText( tr( "Full" ) );
            break;
        case Battery::Discharging:
            ui->batteryStatus->setText( tr( "Discharging" ) );
            break;
        case Battery::Charging:
            ui->batteryStatus->setText( tr( "Charging" ) );
            break;
        default:
            ui->batteryStatus->setText( tr( "No Battery" ) );
            break;
    }
    ui->batteryframe->setVisible(true);

这是编译过程输出的错误：

 make: *** [Makefile:2028: corebox.o] Error 1
 make: *** Waiting for unfinished jobs....
 coreaction/coreaction.cpp: In member function 'void 
 coreaction::batteryCheck()':
 coreaction/coreaction.cpp:114:25: warning: 'b' may be used 
 uninitialized in this function [-Wmaybe-uninitialized]
     switch( b->state() ) {
             ~~~~~~~~^~
 ==> ERROR: A failure occurred in build().
 Aborting...

我做错了什么？

Answer 1

这是重要的部分：

 coreaction/coreaction.cpp:114:25: warning: 'b' may be used 
 uninitialized in this function [-Wmaybe-uninitialized]
     switch( b->state() ) {
             ~~~~~~~~^~

它声明b可以未初始化使用，如果循环为空则会为真，因此b永远不会被设置。

foreach (Battery *bat, *u->batteries()) {
        b = u->batteries()->value(bat->path());
    }

希望有所帮助。解决方案是在将switch语句初始化为nullptr之后在switch语句之前测试b。

这是重要的部分，nullptr和未初始化的指针之间存在差异。

Battery* b = nullptr; // nullptr
Battery* b;           // uninitialized

Answer 2

溶液

Battery *b = nullptr;
    foreach (Battery *bat, *u->batteries()) {
        b = u->batteries()->value(bat->path());
    }
    if (!b)
        return;

qt编程中未初始化的switchcase错误

2 个答案: