no matching function for call to object map(*it);

[ejoshva]

I am trying to make call to a function multiple times but parallelly using QtConcurrent::mapped

But I am not able to over come below error.

error: no matching function for call to object of type 'addWrapper' *result = map(*it); ^~~ The code is as follows

struct addWrapper {
loadbook *instance;
typedef QString result_type;
addWrapper(loadbook *lBook) : instance(lBook) {}
QString operator()(QString &item) {
instance->decrypt->decryptFile(item,'A');
 
}
};
 
addWrapper wrapper(this);
 
QFuture<QString> returnContent = QtConcurrent::mapped(fileList,wrapper);

struct addWrapper {
loadbook *instance;
typedef QString result_type;
addWrapper(loadbook *lBook) : instance(lBook) {}
QString operator()(QString &item) {
instance->decrypt->decryptFile(item,'A');

}
};

addWrapper wrapper(this);

QFuture<QString> returnContent = QtConcurrent::mapped(fileList,wrapper);

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kindly help me resolve this issue.

[wysota]

Why are you complicating things so much?

#include <QtConcurrentMap>
#include <QStringList>
#include <QByteArray>
#include <QFile>
 
struct Decrypter {
  Decrypter(const QByteArray &key) : m_key(key) {}
 
  typedef QByteArray result_type;
 
  QByteArray operator()(const QString &fileName) {
    QFile f(fileName);
    if(!f.open(QIODevice::ReadOnly)) return QByteArray();
    QByteArray result;
    result.reserve(f.size());
    int keyIndex = 0;
    char input;  
    char keyByte;
    while(!f.atEnd()) { 
      f.getChar(&input);
      keyByte = m_key.at(keyIndex);
      keyIndex = (keyIndex+1) % m_key.size();
      result.append( input ^ keyByte );
    }
    return result;
  }
private:
  QByteArray m_key;
};
 
int main() {
  QStringList filesToDecrypt = { "file1", "file2", "file3" };
  QFuture<QByteArray> future = QtConcurrent::mapped(filesToDecrypt, Decrypter("abcdef"));
  return 0;
}

#include <QtConcurrentMap>
#include <QStringList>
#include <QByteArray>
#include <QFile>

struct Decrypter {
  Decrypter(const QByteArray &key) : m_key(key) {}
  
  typedef QByteArray result_type;
  
  QByteArray operator()(const QString &fileName) {
    QFile f(fileName);
    if(!f.open(QIODevice::ReadOnly)) return QByteArray();
    QByteArray result;
    result.reserve(f.size());
    int keyIndex = 0;
    char input;  
    char keyByte;
    while(!f.atEnd()) { 
      f.getChar(&input);
      keyByte = m_key.at(keyIndex);
      keyIndex = (keyIndex+1) % m_key.size();
      result.append( input ^ keyByte );
    }
    return result;
  }
private:
  QByteArray m_key;
};

int main() {
  QStringList filesToDecrypt = { "file1", "file2", "file3" };
  QFuture<QByteArray> future = QtConcurrent::mapped(filesToDecrypt, Decrypter("abcdef"));
  return 0;
}

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[anda_skoa]

I think you have a mismatch in your function signature.
Try a const reference for the operator argument.

Cheers,
_

[ejoshva]

Thank you wysota and anda_skoa for you help.

@Wysota, I have made my decryt() re-entrant.

QString Decrypt::decryptFile(QString sourceFile)
{
    QString decryptedContent;
    decryptedContent.clear();
    string srcFile=sourceFile.toUtf8().constData();
    ifstream ffin;
 
    ffin.open(srcFile.c_str(),ios_base::in|ios_base::binary);
    QChar keystring = 'A';
    char keyToEncryption= keystring.toLatin1();
    if(ffin.is_open())
    {
        char ch;
        while(!(ffin.read(&ch,1).eof()))
        {
            ch ^= keyToEncryption;
            decryptedContent.append(ch);
        }
    }
    ffin.close();
    return decryptedContent;
 
}
 
QString Decrypt::decryptFile(QString sourceFile,QChar keystring)
{
    _decrptedResStr.clear();
    string srcFile=sourceFile.toUtf8().constData();
    ifstream ffin;
 
    ffin.open(srcFile.c_str(),ios_base::in|ios_base::binary);
 
    char keyToEncryption= keystring.toLatin1();
    if(ffin.is_open())
    {
        char ch;
        while(!(ffin.read(&ch,1).eof()))
        {
            ch ^= keyToEncryption;
            _decrptedResStr.append(ch);
        }
    }
    ffin.close();
    return _decrptedResStr;
}

QString Decrypt::decryptFile(QString sourceFile)
{
    QString decryptedContent;
    decryptedContent.clear();
    string srcFile=sourceFile.toUtf8().constData();
    ifstream ffin;

    ffin.open(srcFile.c_str(),ios_base::in|ios_base::binary);
    QChar keystring = 'A';
    char keyToEncryption= keystring.toLatin1();
    if(ffin.is_open())
    {
        char ch;
        while(!(ffin.read(&ch,1).eof()))
        {
            ch ^= keyToEncryption;
            decryptedContent.append(ch);
        }
    }
    ffin.close();
    return decryptedContent;

}

QString Decrypt::decryptFile(QString sourceFile,QChar keystring)
{
    _decrptedResStr.clear();
    string srcFile=sourceFile.toUtf8().constData();
    ifstream ffin;

    ffin.open(srcFile.c_str(),ios_base::in|ios_base::binary);

    char keyToEncryption= keystring.toLatin1();
    if(ffin.is_open())
    {
        char ch;
        while(!(ffin.read(&ch,1).eof()))
        {
            ch ^= keyToEncryption;
            _decrptedResStr.append(ch);
        }
    }
    ffin.close();
    return _decrptedResStr;
}

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I didn't realise what you were telling. Only upon pondering what's wrong got the issue. Now have modified to the first function above. Earlier it was of type 2nd function.

Thank you so much

---

Added after 16 minutes:

@anda_skoa : Thank you so much. You have pointed out exactly. It works now.

QFuture<QString> decryptedContent =  QtConcurrent::mapped(fileList,DecryptMap('A'));
 
struct DecryptMap {
    DecryptMap(const QChar &key) : m_key(key) {}
    typedef QString result_type;
 
    QString operator()(const QString &item)
    {
        Decrypt *decrypt = new Decrypt();
        return decrypt->decryptFile(item,'A');
    }
    QChar m_key;
};

QFuture<QString> decryptedContent =  QtConcurrent::mapped(fileList,DecryptMap('A'));

struct DecryptMap {
    DecryptMap(const QChar &key) : m_key(key) {}
    typedef QString result_type;

    QString operator()(const QString &item)
    {
        Decrypt *decrypt = new Decrypt();
        return decrypt->decryptFile(item,'A');
    }
    QChar m_key;
};

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[anda_skoa]

QString operator()(const QString &item)
    {
        Decrypt *decrypt = new Decrypt();
        return decrypt->decryptFile(item,'A');
    }
};

QString operator()(const QString &item)
    {
        Decrypt *decrypt = new Decrypt();
        return decrypt->decryptFile(item,'A');
    }
};

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You are leaking the Decrypt instance, i.e. there is a "new" but no "delete".
Better create it on the stack, i.e. without new, then it is destroyed when the operator's scope ends.

Cheers,
_

[ejoshva]

@anda_skoa : thanks for pointing it out. will take care now