Best way to initialize QString
I have a QString variable as struct member. What is the best way to initialize it with default value:
struct Foo
{
QString name = "name";
// or
// QString name = QStringLiteral("name");
// or
// QString name = QLatin1String("name");
// or something else...
}
c++ string qt qstring
asked Nov 13 '18 at 11:57
svadumsvadum
235
add a comment |
I have a QString variable as struct member. What is the best way to initialize it with default value:
struct Foo
{
QString name = "name";
// or
// QString name = QStringLiteral("name");
// or
// QString name = QLatin1String("name");
// or something else...
}
c++ string qt qstring
asked Nov 13 '18 at 11:57
svadumsvadum
235
2
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
1
Generally speaking: If you want to initialize aQStringfrom a char*, useQStringLiteral. If you want to pass it to a method, check if that method has an overload forQLatin1String- if yes you can use that one, otherwise fall back toQStringLiteral. The only exception for both cases is an empty string - simply useQString().
– Felix
Nov 13 '18 at 12:06
add a comment |
I have a QString variable as struct member. What is the best way to initialize it with default value:
struct Foo
{
QString name = "name";
// or
// QString name = QStringLiteral("name");
// or
// QString name = QLatin1String("name");
// or something else...
}
c++ string qt qstring
asked Nov 13 '18 at 11:57
svadumsvadum
235
I have a QString variable as struct member. What is the best way to initialize it with default value:
struct Foo
{
QString name = "name";
// or
// QString name = QStringLiteral("name");
// or
// QString name = QLatin1String("name");
// or something else...
}
c++ string qt qstring
c++ string qt qstring
asked Nov 13 '18 at 11:57
svadumsvadum
235
asked Nov 13 '18 at 11:57
svadumsvadum
235
asked Nov 13 '18 at 11:57
svadumsvadum
235
asked Nov 13 '18 at 11:57
svadumsvadum
235
asked Nov 13 '18 at 11:57
svadumsvadum
235
235
2
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
1
Generally speaking: If you want to initialize aQStringfrom a char*, useQStringLiteral. If you want to pass it to a method, check if that method has an overload forQLatin1String- if yes you can use that one, otherwise fall back toQStringLiteral. The only exception for both cases is an empty string - simply useQString().
– Felix
Nov 13 '18 at 12:06
add a comment |
2
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
1
Generally speaking: If you want to initialize aQStringfrom a char*, useQStringLiteral. If you want to pass it to a method, check if that method has an overload forQLatin1String- if yes you can use that one, otherwise fall back toQStringLiteral. The only exception for both cases is an empty string - simply useQString().
– Felix
Nov 13 '18 at 12:06
2
2
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
1
1
Generally speaking: If you want to initialize a
QString from a char*, use QStringLiteral. If you want to pass it to a method, check if that method has an overload for QLatin1String - if yes you can use that one, otherwise fall back to QStringLiteral. The only exception for both cases is an empty string - simply use QString().– Felix
Nov 13 '18 at 12:06
Generally speaking: If you want to initialize a
QString from a char*, use QStringLiteral. If you want to pass it to a method, check if that method has an overload for QLatin1String - if yes you can use that one, otherwise fall back to QStringLiteral. The only exception for both cases is an empty string - simply use QString().– Felix
Nov 13 '18 at 12:06
add a comment |
1 Answer
1
active
oldest
votes
QStringLiteral will have the lowest runtime overhead. It is one of the few literal QString initializations with O(1) cost. QLatin1String will be pretty fast, but have O(N) cost in length of the string. The intiialization with C string literal will have the highest O(N) cost and is equivalent to IIRC QString::fromUtf8("…"). The 2nd and 3rd initialization also adds an O(N) memory cost, since a copy of the string is made (!). Whatever “savings” you made in executable size thus promptly vanish as the program starts up :(
Initialization via QStringLiteral wins, although you may want to leverage modern C++11 custom literals to make it shorter. Resist the urge to use a macro for it: it’d be an extremely misguided approach as you pollute the global namespace with a short symbol.
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
@Mike That's pointless, though.QString str;is all you need: it's a value type, and has a valid value after default-construction.
– Kuba Ober
Nov 14 '18 at 18:34
add a comment |
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1 Answer
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1 Answer
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active
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QStringLiteral will have the lowest runtime overhead. It is one of the few literal QString initializations with O(1) cost. QLatin1String will be pretty fast, but have O(N) cost in length of the string. The intiialization with C string literal will have the highest O(N) cost and is equivalent to IIRC QString::fromUtf8("…"). The 2nd and 3rd initialization also adds an O(N) memory cost, since a copy of the string is made (!). Whatever “savings” you made in executable size thus promptly vanish as the program starts up :(
Initialization via QStringLiteral wins, although you may want to leverage modern C++11 custom literals to make it shorter. Resist the urge to use a macro for it: it’d be an extremely misguided approach as you pollute the global namespace with a short symbol.
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
@Mike That's pointless, though.QString str;is all you need: it's a value type, and has a valid value after default-construction.
– Kuba Ober
Nov 14 '18 at 18:34
add a comment |
QStringLiteral will have the lowest runtime overhead. It is one of the few literal QString initializations with O(1) cost. QLatin1String will be pretty fast, but have O(N) cost in length of the string. The intiialization with C string literal will have the highest O(N) cost and is equivalent to IIRC QString::fromUtf8("…"). The 2nd and 3rd initialization also adds an O(N) memory cost, since a copy of the string is made (!). Whatever “savings” you made in executable size thus promptly vanish as the program starts up :(
Initialization via QStringLiteral wins, although you may want to leverage modern C++11 custom literals to make it shorter. Resist the urge to use a macro for it: it’d be an extremely misguided approach as you pollute the global namespace with a short symbol.
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
@Mike That's pointless, though.QString str;is all you need: it's a value type, and has a valid value after default-construction.
– Kuba Ober
Nov 14 '18 at 18:34
add a comment |
QStringLiteral will have the lowest runtime overhead. It is one of the few literal QString initializations with O(1) cost. QLatin1String will be pretty fast, but have O(N) cost in length of the string. The intiialization with C string literal will have the highest O(N) cost and is equivalent to IIRC QString::fromUtf8("…"). The 2nd and 3rd initialization also adds an O(N) memory cost, since a copy of the string is made (!). Whatever “savings” you made in executable size thus promptly vanish as the program starts up :(
Initialization via QStringLiteral wins, although you may want to leverage modern C++11 custom literals to make it shorter. Resist the urge to use a macro for it: it’d be an extremely misguided approach as you pollute the global namespace with a short symbol.
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
QStringLiteral will have the lowest runtime overhead. It is one of the few literal QString initializations with O(1) cost. QLatin1String will be pretty fast, but have O(N) cost in length of the string. The intiialization with C string literal will have the highest O(N) cost and is equivalent to IIRC QString::fromUtf8("…"). The 2nd and 3rd initialization also adds an O(N) memory cost, since a copy of the string is made (!). Whatever “savings” you made in executable size thus promptly vanish as the program starts up :(
Initialization via QStringLiteral wins, although you may want to leverage modern C++11 custom literals to make it shorter. Resist the urge to use a macro for it: it’d be an extremely misguided approach as you pollute the global namespace with a short symbol.
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
answered Nov 13 '18 at 12:14
Kuba OberKuba Ober
69.7k982187
69.7k982187
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
@Mike That's pointless, though.QString str;is all you need: it's a value type, and has a valid value after default-construction.
– Kuba Ober
Nov 14 '18 at 18:34
add a comment |
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
@Mike That's pointless, though.QString str;is all you need: it's a value type, and has a valid value after default-construction.
– Kuba Ober
Nov 14 '18 at 18:34
QString str (QString());
– Mike
Nov 13 '18 at 20:39
QString str (QString());
– Mike
Nov 13 '18 at 20:39
1
1
@Mike That's pointless, though.
QString str; is all you need: it's a value type, and has a valid value after default-construction.– Kuba Ober
Nov 14 '18 at 18:34
@Mike That's pointless, though.
QString str; is all you need: it's a value type, and has a valid value after default-construction.– Kuba Ober
Nov 14 '18 at 18:34
add a comment |
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2
Good writeup: QStringLiteral explained
– Swordfish
Nov 13 '18 at 11:59
@Swordfish Thanks for the link, interesting article.
– svadum
Nov 13 '18 at 12:05
1
Generally speaking: If you want to initialize a
QStringfrom a char*, useQStringLiteral. If you want to pass it to a method, check if that method has an overload forQLatin1String- if yes you can use that one, otherwise fall back toQStringLiteral. The only exception for both cases is an empty string - simply useQString().– Felix
Nov 13 '18 at 12:06