If we want to avoid allocations, we could just use the const char*, old-school C-style strings. However, that's not very comfortable. Fortunately, the Electronic Arts Standard Template Library (EASTL), a custom implementation of the standard library created for games, contains a fixed size of strings, which won't allocate any additional memory, namely eastl::fixed_string. You can set the maximum size of memory which will be used and, for pathological cases, dynamic allocations can also be enabled.
As long as we don't want to change it, we could also use QStringLiteral for a fixed size string.