Confusing C2065 'undeclared identifier' error

nevdokimof

I have this code:

void AudioBuffer::write(QByteArray *byteArray)
{
    if (!audioData.isEmpty())
        auto frontArray = audioData.front();
    else
    {
        audioData.enqueue(*byteArray);
        return;
    }

    if (frontArray.size() == sizeOfOneArray) // C2065: 'frontArray': undeclared identifier
    {
        audioData.enqueue(*byteArray);
        return;
    }

    if ( (frontArray.size() + byteArray->size()) <= sizeOfOneArray)  // C2065: 'frontArray': undeclared identifier
    {
        frontArray.append(*byteArray); // C2065: 'frontArray': undeclared identifier
        return;
    }
    else
    {
        int32_t remainSize = sizeOfOneArray - frontArray.size();  // C2065: 'frontArray': undeclared identifier

        for(int i = 0; i < remainSize; ++i)
        {
              //some work
        }
    }

}

frontArray has been declared but QtCreator somehow isn't sure about it

I believe it has smth to do with declaration in if statement because if I declare frontArrayoutside of it it works just fine. In my case it's ok to declare frontArray there, if audioDatais empty function just returns and don't do anything with undeclared variable.
Declaring frontArray also in else statement doesn't change anything.

Header file:

#include <QObject>
#include <QQueue>

class AudioBuffer : public QObject
{
    Q_OBJECT

private:
    QQueue<QByteArray> audioData;

    int32_t sizeOfOneArray = 50 * 32;

public:

    explicit AudioBuffer(QObject *parent = nullptr);
    AudioBuffer (int32_t _sizeOfOneArray, QObject *parent = nullptr);

    QByteArray read();
    void write(QByteArray* byteArray);

};

Qt Creator 4.7.0, compiler is MSVC 2015

mzimmers

I believe your analysis is correct -- the problem is that the variable is defined within an invisible unit that consists only of the declaration of the variable itself. In other words, it's gone immediately after it's defined.

There are several fixes; the simplest one (though not necessarily the best example of coding) is this:

void AudioBuffer::write(QByteArray *byteArray)
{
    if (audioData.isEmpty())
        audioData.enqueue(*byteArray);
        return;
    }

    auto frontArray = audioData.front();
    if (frontArray.size() == sizeOfOneArray) 
    {
...

nevdokimof

Yep, frontArray just goes out of scope. Thanks.

Cpp reference says:

if (x)
    int i;
// i is no longer in scope