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 Types

typedef const_iterator
typedef const_reference
typedef const_reverse_iterator
typedef difference_type
typedef iterator
typedef reference
typedef reverse_iterator
typedef size_type
typedef value_type

Detailed Description

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 Type Documentation

typedef QLatin1String::const_iterator

This typedef provides an STL-style const iterator for QLatin1String.

This typedef was introduced in Qt 5.10.

See also iterator and const_reverse_iterator.

typedef QLatin1String::const_reference

Alias for reference. Provided for compatibility with the STL.

This typedef was introduced in Qt 5.11.

typedef QLatin1String::const_reverse_iterator

This typedef provides an STL-style const reverse iterator for QLatin1String.

This typedef was introduced in Qt 5.10.

See also reverse_iterator and const_iterator.

typedef QLatin1String::difference_type

Alias for int. Provided for compatibility with the STL.

This typedef was introduced in Qt 5.10.

typedef QLatin1String::iterator

This typedef provides an STL-style const iterator for QLatin1String.

QLatin1String does not support mutable iterators, so this is the same as const_iterator.

This typedef was introduced in Qt 5.10.

See also const_iterator and reverse_iterator.

typedef QLatin1String::reference

Alias for value_type &. Provided for compatibility with the STL.

This typedef was introduced in Qt 5.10.

typedef QLatin1String::reverse_iterator

This typedef provides an STL-style const reverse iterator for QLatin1String.

QLatin1String does not support mutable reverse iterators, so this is the same as const_reverse_iterator.

This typedef was introduced in Qt 5.10.

See also const_reverse_iterator and iterator.

typedef QLatin1String::size_type

Alias for int. Provided for compatibility with the STL.

This typedef was introduced in Qt 5.10.

typedef QLatin1String::value_type

Alias for const char. Provided for compatibility with the STL.

This typedef was introduced in Qt 5.10.