qiodevice.cpp

QT 开发环境里面一个很重要的文件

                // optimization to avoid initial self-assignment
                while (*readPtr != '\r') {
                    if (++readPtr == endPtr)
                        return readSoFar;
                }

                char *writePtr = readPtr;

                while (readPtr < endPtr) {
                    char ch = *readPtr++;
                    if (ch != '\r')
                        *writePtr++ = ch;
                    else
                        --readSoFar;
                }

                // Make sure we get more data if there is room for more. This
                // is very important for when someone seeks to the start of a
                // '\r\n' and reads one character - they should get the '\n'.
                moreToRead = (readPtr != writePtr);
            }
        }
    } while (moreToRead);

#if defined QIODEVICE_DEBUG
    printf("%p \treturning %d, d->pos == %d, d->buffer.size() == %d\n", this,
           int(readSoFar), int(d->pos), d->buffer.size());
    debugBinaryString(data, readSoFar);
#endif
    return readSoFar;
}

/*!
    \overload

    Reads at most \a maxSize bytes from the device, and returns the
    data read as a QByteArray.

    This function has no way of reporting errors; returning an empty
    QByteArray() can mean either that no data was currently available
    for reading, or that an error occurred.
*/
QByteArray QIODevice::read(qint64 maxSize)
{
    Q_D(QIODevice);
    CHECK_MAXLEN(read, QByteArray());
    QByteArray tmp;
    qint64 readSoFar = 0;
    char buffer[4096];
#if defined QIODEVICE_DEBUG
    printf("%p QIODevice::read(%d), d->pos = %d, d->buffer.size() = %d\n",
           this, int(maxSize), int(d->pos), int(d->buffer.size()));
#else
    Q_UNUSED(d);
#endif

    do {
        qint64 bytesToRead = qMin(int(maxSize - readSoFar), int(sizeof(buffer)));
        qint64 readBytes = read(buffer, bytesToRead);
        if (readBytes <= 0)
            break;
        tmp += QByteArray(buffer, (int) readBytes);
        readSoFar += readBytes;
    } while (readSoFar < maxSize && bytesAvailable() > 0);

    return tmp;
}

/*!
    \overload

    Reads all available data from the device, and returns it as a
    QByteArray.

    This function has no way of reporting errors; returning an empty
    QByteArray() can mean either that no data was currently available
    for reading, or that an error occurred.
*/
QByteArray QIODevice::readAll()
{
    Q_D(QIODevice);
#if defined QIODEVICE_DEBUG
    printf("%p QIODevice::readAll(), d->pos = %d, d->buffer.size() = %d\n",
           this, int(d->pos), int(d->buffer.size()));
#endif

    QByteArray tmp;
    if (d->isSequential() || size() == 0) {
        // Read it in chunks, bytesAvailable() is unreliable for sequential
        // devices.
        const int chunkSize = 4096;
        qint64 totalRead = 0;
        forever {
            tmp.resize(tmp.size() + chunkSize);
            qint64 readBytes = read(tmp.data() + totalRead, chunkSize);
            tmp.chop(chunkSize - (readBytes < 0 ? 0 : readBytes));
            if (readBytes <= 0)
                return tmp;
            totalRead += readBytes;
        }
    } else {
        // Read it all in one go.
        tmp.resize(int(bytesAvailable()));
        qint64 readBytes = read(tmp.data(), tmp.size());
        tmp.resize(readBytes < 0 ? 0 : int(readBytes));
    }
    return tmp;
}

/*!
    This function reads a line of ASCII characters from the device, up to a
    maximum of \a maxSize - 1 bytes, stores the characters in \a data, and
    returns the number of bytes read. If an error occurred, -1 is returned.

    A terminating '\0' byte is always appended to \a data, so \a
    maxSize must be larger than 1.

    Data is read until either of the following conditions are met:

    \list
    \o The first '\n' character is read.
    \o \a maxSize - 1 bytes are read.
    \o The end of the device data is detected.
    \endlist

    For example, the following code reads a line of characters from a
    file:

    \code
        QFile file("box.txt");
        if (file.open(QFile::ReadOnly)) {
            char buf[1024];
            qint64 lineLength = file.readLine(buf, sizeof(buf));
            if (lineLength != -1) {
                // the line is available in buf
            }
        }
    \endcode

    If the '\n' character is the 1023th character read then it will be
    inserted into the buffer; if it occurs after the 1023 character then
    it is not read.

    This function calls readLineData(), which is implemented using
    repeated calls to getChar(). You can provide a more efficient
    implementation by reimplementing readLineData() in your own
    subclass.

    \sa getChar(), read(), write()
*/
qint64 QIODevice::readLine(char *data, qint64 maxSize)
{
    Q_D(QIODevice);
    if (maxSize < 2) {
        qWarning("QIODevice::readLine: Called with maxSize < 2");
        return qint64(-1);
    }

#if defined QIODEVICE_DEBUG
    printf("%p QIODevice::readLine(%p, %d), d->pos = %d, d->buffer.size() = %d\n",
           this, data, int(maxSize), int(d->pos), int(d->buffer.size()));
#endif

    // Leave room for a '\0'
    --maxSize;

    const bool sequential = d->isSequential();

    qint64 readSoFar = 0;
    if (!d->buffer.isEmpty()) {
        readSoFar = d->buffer.readLine(data, maxSize);
        if (!sequential)
            d->pos += readSoFar;
#if defined QIODEVICE_DEBUG
        printf("%p \tread from buffer: %d bytes, last character read: %hhx\n", this,
               int(readSoFar), data[int(readSoFar) - 1]);
        if (readSoFar)
            debugBinaryString(data, int(readSoFar));
#endif
        if (readSoFar && data[readSoFar - 1] == '\n') {
            data[readSoFar] = '\0';
            return readSoFar;
        }
    }

    if (d->pos != d->devicePos && !sequential && !seek(d->pos))
        return qint64(-1);
    d->baseReadLineDataCalled = false;
    qint64 readBytes = readLineData(data + readSoFar, maxSize - readSoFar);
#if defined QIODEVICE_DEBUG
    printf("%p \tread from readLineData: %d bytes, readSoFar = %d bytes\n", this,
           int(readBytes), int(readSoFar));
    if (readBytes > 0) {
        debugBinaryString(data, int(readSoFar + readBytes));
    }
#endif
    if (readBytes <= 0) {
        data[readSoFar] = '\0';
        return readSoFar ? readSoFar : -1;
    }
    readSoFar += readBytes;
    if (!d->baseReadLineDataCalled && !sequential) {
        d->pos += readBytes;
        // If the base implementation was not called, then we must
        // assume the device position is invalid and force a seek.
        d->devicePos = qint64(-1);
    }
    data[readSoFar] = '\0';

    if (d->openMode & Text) {
        if (readSoFar > 1 && data[readSoFar - 1] == '\n' && data[readSoFar - 2] == '\r') {
            data[readSoFar - 2] = '\n';
            data[readSoFar - 1] = '\0';
            --readSoFar;
        }
    }

#if defined QIODEVICE_DEBUG
    printf("%p \treturning %d, d->pos = %d, d->buffer.size() = %d, size() = %d\n",
           this, int(readSoFar), int(d->pos), d->buffer.size(), int(size()));
    debugBinaryString(data, int(readSoFar));
#endif
    return readSoFar;
}

/*!
    \overload

    Reads a line from the device, but no more than \a maxSize characters,
    and returns the result as a QByteArray.

    This function has no way of reporting errors; returning an empty
    QByteArray() can mean either that no data was currently available
    for reading, or that an error occurred.
*/
QByteArray QIODevice::readLine(qint64 maxSize)
{
    Q_D(QIODevice);
    CHECK_MAXLEN(readLine, QByteArray());
    QByteArray tmp;
    const int BufferGrowth = 4096;
    qint64 readSoFar = 0;
    qint64 readBytes = 0;

#if defined QIODEVICE_DEBUG
    printf("%p QIODevice::readLine(%d), d->pos = %d, d->buffer.size() = %d\n",
           this, int(maxSize), int(d->pos), int(d->buffer.size()));
#else
    Q_UNUSED(d);
#endif

    do {
        if (maxSize != 0)
            tmp.resize(int(readSoFar + qMin(int(maxSize), BufferGrowth)));
        else
            tmp.resize(int(readSoFar + BufferGrowth));
        readBytes = readLine(tmp.data() + readSoFar, tmp.size() - readSoFar);
        if (readBytes <= 0)
            break;

        readSoFar += readBytes;
    } while ((!maxSize || readSoFar < maxSize) &&
             readSoFar + 1 == tmp.size() &&   // +1 due to the ending null
             tmp.at(readSoFar - 1) != '\n');

    tmp.resize(int(readSoFar));
    return tmp;
}

/*!
    Reads up to \a maxSize characters into \a data and returns the
    number of characters read.

    This function is called by readLine(), and provides its base
    implementation, using getChar(). Buffered devices can improve the
    performance of readLine() by reimplementing this function.

    readLine() appends a '\0' byte to \a data; readLineData() does not
    need to do this.
*/
qint64 QIODevice::readLineData(char *data, qint64 maxSize)
{
    qint64 readSoFar = 0;
    char c;
    bool lastGetSucceeded = false;
    d_func()->baseReadLineDataCalled = true;

    while (readSoFar < maxSize && (lastGetSucceeded = getChar(&c))) {
        *data++ = c;
        ++readSoFar;
        if (c == '\n')
            break;
    }

#if defined QIODEVICE_DEBUG
    Q_D(QIODevice);
    printf("%p QIODevice::readLineData(%p, %d), d->pos = %d, d->buffer.size() = %d, returns %d\n",
           this, data, int(maxSize), int(d->pos), int(d->buffer.size()), int(readSoFar));
#endif
    if (!lastGetSucceeded && readSoFar == 0)
        return qint64(-1);
    return readSoFar;
}

/*!
    Returns true if a complete line of data can be read from the device;
    otherwise returns false.

    Note that unbuffered devices, which have no way of determining what
    can be read, always return false.

    This function is often called in conjunction with the readyRead()
    signal.

    Subclasses that reimplement this function must call the base
    implementation in order to include the size of the QIODevice's buffer. Example:

    \code
        bool CustomDevice::canReadLine() const
        {
            return buffer.contains('\n') || QIODevice::canReadLine();
        }
    \endcode

    \sa readyRead(), readLine()
*/
bool QIODevice::canReadLine() const
{
    return d_func()->buffer.canReadLine();
}

/*! \fn bool QIODevice::getChar(char *c)

    Reads one character from the device and stores it in \a c. If \a c
    is 0, the character is discarded. Returns true on success;
    otherwise returns false.

    \sa read() putChar() ungetChar()
*/

/*!
    Writes at most \a maxSize bytes of data from \a data to the
    device. Returns the number of bytes that were actually written, or
    -1 if an error occurred.

    \sa read() writeData()
*/
qint64 QIODevice::write(const char *data, qint64 maxSize)
{
    Q_D(QIODevice);
    CHECK_OPEN(write, qint64(-1));
    CHECK_WRITABLE(write, qint64(-1));
    CHECK_MAXLEN(write, qint64(-1));

    const bool sequential = d->isSequential();
    // Make sure the device is positioned correctly.
    if (d->pos != d->devicePos && !sequential && !seek(d->pos))
        return qint64(-1);

#ifdef Q_OS_WIN
    if (d->openMode & Text) {
        const char *endOfData = data + maxSize;
        const char *startOfBlock = data;

        qint64 writtenSoFar = 0;

        forever {
            const char *endOfBlock = startOfBlock;
            while (endOfBlock < endOfData && *endOfBlock != '\n')
                ++endOfBlock;

            qint64 blockSize = endOfBlock - startOfBlock;
            if (blockSize > 0) {
                qint64 ret = writeData(startOfBlock, blockSize);
                if (ret <= 0) {
                    if (writtenSoFar && !sequential)
                        d->buffer.skip(writtenSoFar);
                    return writtenSoFar ? writtenSoFar : ret;
                }
                if (!sequential) {
                    d->pos += ret;
                    d->devicePos += ret;
                }
                writtenSoFar += ret;
            }

            if (endOfBlock == endOfData)
                break;

            qint64 ret = writeData("\r\n", 2);
            if (ret <= 0) {
                if (writtenSoFar && !sequential)
                    d->buffer.skip(writtenSoFar);
                return writtenSoFar ? writtenSoFar : ret;
            }
            if (!sequential) {
                d->pos += ret;
                d->devicePos += ret;
            }
            ++writtenSoFar;

            startOfBlock = endOfBlock + 1;
        }

        if (writtenSoFar && !sequential)
            d->buffer.skip(writtenSoFar);
        return writtenSoFar;
    }
#endif

    qint64 written = writeData(data, maxSize);
    if (written > 0) {