QTextStream Class

See also QDataStream, QIODevice, QFile, QBuffer, QTcpSocket

This enum specifies how to align text in fields when the field is wider than the text that occupies it.

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flags QTextStream::NumberFlags

This enum specifies various flags that can be set to affect the output of integers, floats, and doubles.

The NumberFlags type is a typedef for QFlags<NumberFlag>. It stores an OR combination of NumberFlag values.

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This enum specifies which notations to use for expressing float and double as strings.

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This enum describes the current status of the text stream.

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Constructs a QTextStream. Before you can use it for reading or writing, you must assign a device or a string.

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Constructs a QTextStream that operates on device.

Constructs a QTextStream that operates on fileHandle, using openMode to define the open mode. Internally, a QFile is created to handle the FILE pointer.

This constructor is useful for working directly with the common FILE based input and output streams: stdin, stdout and stderr. Example:

QString str;
QTextStream in(stdin);
in >> str;

Constructs a QTextStream that operates on string, using openMode to define the open mode.

Constructs a QTextStream that operates on array, using openMode to define the open mode. Internally, the array is wrapped by a QBuffer.

Constructs a QTextStream that operates on array, using openMode to define the open mode. The array is accessed as read-only, regardless of the values in openMode.

This constructor is convenient for working on constant strings. Example:

int main(int argc, char *argv[])
{
    // read numeric arguments (123, 0x20, 4.5...)
    for (int i = 1; i < argc; ++i) {
          int number;
          QTextStream in(argv[i]);
          in >> number;
          ...
    }
}

Destroys the QTextStream.

If the stream operates on a device, flush() will be called implicitly. Otherwise, the device is unaffected.

Returns true if there is no more data to be read from the QTextStream; otherwise returns false. This is similar to, but not the same as calling QIODevice::atEnd(), as QTextStream also takes into account its internal Unicode buffer.

Returns true if automatic Unicode detection is enabled, otherwise returns false. Automatic Unicode detection is enabled by default.

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Returns the current device associated with the QTextStream, or nullptr if no device has been assigned.

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Returns the encoding that is current assigned to the stream.

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Returns the current field alignment.

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Returns the current field width.

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Flushes any buffered data waiting to be written to the device.

If QTextStream operates on a string, this function does nothing.

Returns true if QTextStream is set to generate the UTF BOM (Byte Order Mark) when using a UTF encoding; otherwise returns false. UTF BOM generation is set to false by default.

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Returns the current base of integers. 0 means that the base is detected when reading, or 10 (decimal) when generating numbers.

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Returns the locale for this stream. The default locale is C.

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Returns the current number flags.

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Returns the current pad character.

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Returns the device position corresponding to the current position of the stream, or -1 if an error occurs (e.g., if there is no device or string, or if there's a device error).

Because QTextStream is buffered, this function may have to seek the device to reconstruct a valid device position. This operation can be expensive, so you may want to avoid calling this function in a tight loop.

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Reads at most maxlen characters from the stream, and returns the data read as a QString.

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Reads the entire content of the stream, and returns it as a QString. Avoid this function when working on large files, as it will consume a significant amount of memory.

Calling readLine() is better if you do not know how much data is available.

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Reads one line of text from the stream, and returns it as a QString. The maximum allowed line length is set to maxlen. If the stream contains lines longer than this, then the lines will be split after maxlen characters and returned in parts.

If maxlen is 0, the lines can be of any length.

The returned line has no trailing end-of-line characters ("\n" or "\r\n"), so calling QString::trimmed() can be unnecessary.

If the stream has read to the end of the file, readLine() will return a null QString. For strings, or for devices that support it, you can explicitly test for the end of the stream using atEnd().

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Reads one line of text from the stream into line. If line is nullptr, the read line is not stored.

The maximum allowed line length is set to maxlen. If the stream contains lines longer than this, then the lines will be split after maxlen characters and returned in parts.

If maxlen is 0, the lines can be of any length.

The resulting line has no trailing end-of-line characters ("\n" or "\r\n"), so calling QString::trimmed() can be unnecessary.

If line has sufficient capacity for the data that is about to be read, this function may not need to allocate new memory. Because of this, it can be faster than readLine().

Returns false if the stream has read to the end of the file or an error has occurred; otherwise returns true. The contents in line before the call are discarded in any case.

This function was introduced in Qt 5.5.

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Returns the current real number notation.

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Returns the current real number precision, or the number of fraction digits QTextStream will write when generating real numbers (FixedNotation, ScientificNotation), or the maximum number of significant digits (SmartNotation).

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Resets QTextStream's formatting options, bringing it back to its original constructed state. The device, string and any buffered data is left untouched.

Resets the status of the text stream.

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Seeks to the position pos in the device. Returns true on success; otherwise returns false.

If enabled is true, QTextStream will attempt to detect Unicode encoding by peeking into the stream data to see if it can find the UTF-8, UTF-16, or UTF-32 Byte Order Mark (BOM). If this mark is found, QTextStream will replace the current encoding with the UTF encoding.

This function can be used together with setEncoding(). It is common to set the encoding to UTF-8, and then enable UTF-16 detection.

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Sets the current device to device. If a device has already been assigned, QTextStream will call flush() before the old device is replaced.

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Sets the encoding for this stream to encoding. The encoding is used for decoding any data that is read from the assigned device, and for encoding any data that is written. By default, QStringConverter::Utf8 is used, and automatic unicode detection is enabled.

If QTextStream operates on a string, this function does nothing.

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Sets the field alignment to mode. When used together with setFieldWidth(), this function allows you to generate formatted output with text aligned to the left, to the right or center aligned.

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Sets the current field width to width. If width is 0 (the default), the field width is equal to the length of the generated text.

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If generate is true and a UTF encoding is used, QTextStream will insert the BOM (Byte Order Mark) before any data has been written to the device. If generate is false, no BOM will be inserted. This function must be called before any data is written. Otherwise, it does nothing.

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Sets the base of integers to base, both for reading and for generating numbers. base can be either 2 (binary), 8 (octal), 10 (decimal) or 16 (hexadecimal). If base is 0, QTextStream will attempt to detect the base by inspecting the data on the stream. When generating numbers, QTextStream assumes base is 10 unless the base has been set explicitly.

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Sets the locale for this stream to locale. The specified locale is used for conversions between numbers and their string representations.

The default locale is C and it is a special case - the thousands group separator is not used for backward compatibility reasons.

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Sets the current number flags to flags. flags is a set of flags from the NumberFlag enum, and describes options for formatting generated code (e.g., whether or not to always write the base or sign of a number).

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Sets the pad character to ch. The default value is the ASCII space character (' '), or QChar(0x20). This character is used to fill in the space in fields when generating text.

Example:

QString s;
QTextStream out(&s);
out.setFieldWidth(10);
out.setFieldAlignment(QTextStream::AlignCenter);
out.setPadChar('-');
out << "Qt" << "rocks!";

The string s contains:

----Qt------rocks!--

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Sets the real number notation to notation (SmartNotation, FixedNotation, ScientificNotation). When reading and generating numbers, QTextStream uses this value to detect the formatting of real numbers.

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Sets the precision of real numbers to precision. This value describes the number of fraction digits QTextStream should write when generating real numbers (FixedNotation, ScientificNotation), or the maximum number of significant digits (SmartNotation).

The precision cannot be a negative value. The default value is 6.

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Sets the status of the text stream to the status given.

Subsequent calls to setStatus() are ignored until resetStatus() is called.

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Sets the current string to string, using the given openMode. If a device has already been assigned, QTextStream will call flush() before replacing it.

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Reads and discards whitespace from the stream until either a non-space character is detected, or until atEnd() returns true. This function is useful when reading a stream character by character.

Whitespace characters are all characters for which QChar::isSpace() returns true.

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Returns the status of the text stream.

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Returns the current string assigned to the QTextStream, or nullptr if no string has been assigned.

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Writes the character c to the stream, then returns a reference to the QTextStream.

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This is an overloaded function.

Converts c from ASCII to a QChar, then writes it to the stream.

This is an overloaded function.

Writes the Unicode character c to the stream, then returns a reference to the QTextStream.

This function was introduced in Qt 6.3.1.

Writes the integer number i to the stream, then returns a reference to the QTextStream. By default, the number is stored in decimal form, but you can also set the base by calling setIntegerBase().

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This is an overloaded function.

Writes the unsigned short i to the stream.

This is an overloaded function.

Writes the signed int i to the stream.

This is an overloaded function.

Writes the unsigned int i to the stream.

This is an overloaded function.

Writes the signed long i to the stream.

This is an overloaded function.

Writes the unsigned long i to the stream.

This is an overloaded function.

Writes the qlonglong i to the stream.

This is an overloaded function.

Writes the qulonglong i to the stream.

Writes the real number f to the stream, then returns a reference to the QTextStream. By default, QTextStream stores it using SmartNotation, with up to 6 digits of precision. You can change the textual representation QTextStream will use for real numbers by calling setRealNumberNotation(), setRealNumberPrecision() and setNumberFlags().

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This is an overloaded function.

Writes the double f to the stream.

Writes the string string to the stream, and returns a reference to the QTextStream. The string is first encoded using the assigned encoding (the default is UTF-8) before it is written to the stream.

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This is an overloaded function.

Writes string to the stream, and returns a reference to the QTextStream.

This function was introduced in Qt 5.12.

This is an overloaded function.

Writes string to the stream, and returns a reference to the QTextStream.

This is an overloaded function.

Writes array to the stream. The contents of array are converted with QString::fromUtf8().

This is an overloaded function.

Writes the constant string pointed to by string to the stream. string is assumed to be in UTF-8 encoding. This operator is convenient when working with constant string data. Example:

QTextStream out(stdout);
out << "Qt rocks!" << Qt::endl;

Warning: QTextStream assumes that string points to a string of text, terminated by a '\0' character. If there is no terminating '\0' character, your application may crash.

This is an overloaded function.

Writes ptr to the stream as a hexadecimal number with a base.

Reads a character from the stream and stores it in c. Returns a reference to the QTextStream, so several operators can be nested. Example:

QTextStream in(file);
QChar ch1, ch2, ch3;
in >> ch1 >> ch2 >> ch3;

Whitespace is not skipped.

This is an overloaded function.

Reads a character from the stream and stores it in c. The character from the stream is converted to ISO-5589-1 before it is stored.

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This is an overloaded function.

Reads a character from the stream and stores it in c.

This function was introduced in Qt 6.4.

Reads an integer from the stream and stores it in i, then returns a reference to the QTextStream. The number is cast to the correct type before it is stored. If no number was detected on the stream, i is set to 0.

By default, QTextStream will attempt to detect the base of the number using the following rules:

By calling setIntegerBase(), you can specify the integer base explicitly. This will disable the auto-detection, and speed up QTextStream slightly.

Leading whitespace is skipped.

This is an overloaded function.

Stores the integer in the unsigned short i.

This is an overloaded function.

Stores the integer in the signed int i.

This is an overloaded function.

Stores the integer in the unsigned int i.

This is an overloaded function.

Stores the integer in the signed long i.

This is an overloaded function.

Stores the integer in the unsigned long i.

This is an overloaded function.

Stores the integer in the qlonglong i.

This is an overloaded function.

Stores the integer in the qulonglong i.

Reads a real number from the stream and stores it in f, then returns a reference to the QTextStream. The number is cast to the correct type. If no real number is detect on the stream, f is set to 0.0.

As a special exception, QTextStream allows the strings "nan" and "inf" to represent NAN and INF floats or doubles.

Leading whitespace is skipped.

This is an overloaded function.

Stores the real number in the double f.

Reads a word from the stream and stores it in str, then returns a reference to the stream. Words are separated by whitespace (i.e., all characters for which QChar::isSpace() returns true).

Leading whitespace is skipped.

This is an overloaded function.

Converts the word to UTF-8, then stores it in array.

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This is an overloaded function.

Converts the word to UTF-8 and stores it in c, terminated by a '\0' character. If no word is available, only the '\0' character is stored.

Warning: Although convenient, this operator is dangerous and must be used with care. QTextStream assumes that c points to a buffer with enough space to hold the word. If the buffer is too small, your application may crash. For a word consisting of n QChars, the buffer needs to be at least 3*n+1 characters long.

If possible, use the QByteArray operator instead.

Equivalent to QTextStream::setFieldWidth(width).

Equivalent to QTextStream::setPadChar(ch).

Equivalent to QTextStream::setRealNumberPrecision(precision).