FName
When you name a new asset in the Content Browser, change a parameter in a Dynamic Material Instance, or access a bone in a Skeletal Mesh, you are using FNames. FNames provide a very lightweight system for using strings, where a given string is stored only once in a data table, even if it is reused.
FNames are case-insensitive. They are immutable, and cannot be manipulated. The storage system and static nature of FNames means that it is fast to look up and access FNames with keys. Another feature of the FName subsystem is the use of a hash table to provide fast string to FName conversions.
FText
In Unreal Engine 4 (UE4) the primary component for text localization is the FText class. All user-facing text should use this class, as it supports text localization by providing the following features:
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Formatting Text (to generate text from a placeholder pattern).
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Generating derived text, such as making text upper or lower case.
FText also features the AsCultureInvariant function (or the INVTEXT macro), which creates non-localized, or "culture invariant" text. This is useful for things like converting a player name from an external API into something you can display in your user interface.
You can create a blank FText using either FText::GetEmpty(), or by using just FText().
FString
Unlike FName and FText, FString can be searched, modified, and compared against other strings. However, these manipulations can make FStrings more expensive than the immutable string classes. This is because FString objects store their own character arrays, while FName and FText objects store an index to a shared character array, and can establish equality based purely on this index value.
Printf
The FString function, Printf, can create FString objects the format argument specifiers as the C++ printf function. Similarly, the UE_LOG macro prints a printf formatted string to the screen, log output, and log files, depending on what type of UE4 build is running.
Remember that to use these strings and conversion you will need to include the necessary header files. A list of which header files are needed can be found on the API reference page for each string.
Conversions
|From | To | Example | |---|------|---------|%fnametofstring% %fnametoftext% %fstringtofname% %fstringtoftext% %ftexttofstring% %ftexttofname% %fstringtoint32% %fstringtofloat% %int32tofstring% %floattofstring%
Encoding
In general, you should be using the TEXT() macro when setting string variable literals. If you do not specify the TEXT() macro, your literal will be encoded using ANSI, which is highly limited in what characters it supports. Any ANSI literals being passed into FString need to undergo a conversion to TCHAR (native Unicode encoding), so it is more efficient to use TEXT().
For more about encoding, see the Character Encoding documentation.