Contents

QLatin1String Class

The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal. More...

Header: #include <QLatin1String>
qmake: QT += core

Note: All functions in this class are reentrant.

Public Functions

QLatin1Char at(int pos) const
QLatin1Char back() const
QLatin1Char front() const
bool operator!=(const char *other) const
bool operator!=(const QByteArray &other) const
bool operator<(const char *other) const
bool operator<(const QByteArray &other) const
bool operator<=(const char *other) const
bool operator<=(const QByteArray &other) const
bool operator==(const char *other) const
bool operator==(const QByteArray &other) const
bool operator>(const char *other) const
bool operator>(const QByteArray &other) const
bool operator>=(const char *other) const
bool operator>=(const QByteArray &other) const
QLatin1Char operator[](int pos) const

Detailed Description

The QLatin1String class provides a thin wrapper around an US-ASCII/Latin-1 encoded string literal.

Many of QString's member functions are overloaded to accept const char * instead of QString. This includes the copy constructor, the assignment operator, the comparison operators, and various other functions such as insert(), replace(), and indexOf(). These functions are usually optimized to avoid constructing a QString object for the const char * data. For example, assuming str is a QString,

 if (str == "auto" || str == "extern"
         || str == "static" || str == "register") {
     ...
 }

is much faster than

 if (str == QString("auto") || str == QString("extern")
         || str == QString("static") || str == QString("register")) {
     ...
 }

because it doesn't construct four temporary QString objects and make a deep copy of the character data.

Applications that define QT_NO_CAST_FROM_ASCII (as explained in the QString documentation) don't have access to QString's const char * API. To provide an efficient way of specifying constant Latin-1 strings, Qt provides the QLatin1String, which is just a very thin wrapper around a const char *. Using QLatin1String, the example code above becomes

 if (str == QLatin1String("auto")
         || str == QLatin1String("extern")
         || str == QLatin1String("static")
         || str == QLatin1String("register") {
     ...
 }

This is a bit longer to type, but it provides exactly the same benefits as the first version of the code, and is faster than converting the Latin-1 strings using QString::fromLatin1().

Thanks to the QString(QLatin1String) constructor, QLatin1String can be used everywhere a QString is expected. For example:

 QLabel *label = new QLabel(QLatin1String("MOD"), this);

Note: If the function you're calling with a QLatin1String argument isn't actually overloaded to take QLatin1String, the implicit conversion to QString will trigger a memory allocation, which is usually what you want to avoid by using QLatin1String in the first place. In those cases, using QStringLiteral may be the better option.

See also QString, QLatin1Char, QStringLiteral, and QT_NO_CAST_FROM_ASCII.

Member Function Documentation

QLatin1Char QLatin1String::at(int pos) const

Returns the character at position pos in this object.

Note: This function performs no error checking. The behavior is undefined when pos < 0 or pos >= size().

This function was introduced in Qt 5.8.

See also operator[]().

QLatin1Char QLatin1String::back() const

Returns the last character in the string. Same as at(size() - 1).

This function is provided for STL compatibility.

Warning: Calling this function on an empty string constitutes undefined behavior.

This function was introduced in Qt 5.10.

See also front(), at(), and operator[]().

QLatin1Char QLatin1String::front() const

Returns the first character in the string. Same as at(0).

This function is provided for STL compatibility.

Warning: Calling this function on an empty string constitutes undefined behavior.

This function was introduced in Qt 5.10.

See also back(), at(), and operator[]().

bool QLatin1String::operator!=(const char *other) const

This function overloads operator!=().

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator!=(const QByteArray &other) const

This function overloads operator!=().

The other byte array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator<(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator<(const QByteArray &other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator<=(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator<=(const QByteArray &other) const

This is an overloaded function.

The other array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator==(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator==(const QByteArray &other) const

This is an overloaded function.

The other byte array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator>(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator>(const QByteArray &other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator>=(const char *other) const

This is an overloaded function.

The other const char pointer is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 4.3.

See also QT_NO_CAST_FROM_ASCII.

bool QLatin1String::operator>=(const QByteArray &other) const

This is an overloaded function.

The other array is converted to a QString using the QString::fromUtf8() function.

You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

This function was introduced in Qt 5.0.

See also QT_NO_CAST_FROM_ASCII.

QLatin1Char QLatin1String::operator[](int pos) const

Returns the character at position pos in this object.

Note: This function performs no error checking. The behavior is undefined when pos < 0 or pos >= size().

This function was introduced in Qt 5.8.

See also at().

© 2023 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners.
The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation.
Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.