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# String conversions
Catch needs to be able to convert types you use in assertions and logging expressions into strings (for logging and reporting purposes).
Most built-in or std types are supported out of the box but there are three ways that you can tell Catch how to convert your own types (or other, third-party types) into strings.
## operator << overload for std::ostream
This is the standard way of providing string conversions in C++ - and the chances are you may already provide this for your own purposes. If you're not familiar with this idiom it involves writing a free function of the form:
```
std::ostream& operator << ( std::ostream& os, T const& value ) {
os << convertMyTypeToString( value );
return os;
}
```
(where ```T``` is your type and ```convertMyTypeToString``` is where you'll write whatever code is necessary to make your type printable - it doesn't have to be in another function).
You should put this function in the same namespace as your type.
Alternatively you may prefer to write it as a member function:
```
std::ostream& T::operator << ( std::ostream& os ) const {
os << convertMyTypeToString( *this );
return os;
}
```
## Catch::toString overload
If you don't want to provide an ```operator <<``` overload, or you want to convert your type differently for testing purposes, you can provide an overload for ```Catch::toString()``` for your type.
```
namespace Catch {
std::string toString( T const& value ) {
return convertMyTypeToString( value );
}
}
```
Again ```T``` is your type and ```convertMyTypeToString``` is where you'll write whatever code is necessary to make your type printable. Note that the function must be in the Catch namespace, which itself must be in the global namespace.
## Catch::StringMaker<T> specialisation
There are some cases where overloading toString does not work as expected. Specialising StringMaker<T> gives you more precise, and reliable, control - but at the cost of slightly more code and complexity:
```
namespace Catch {
template<> struct StringMaker<T> {
static std::string convert( T const& value ) {
return convertMyTypeToString( value );
}
};
}
```
## Exceptions
By default all exceptions deriving from `std::exception` will be translated to strings by calling the `what()` method. For exception types that do not derive from `std::exception` - or if `what()` does not return a suitable string - use `CATCH_TRANSLATE_EXCEPTION`. This defines a function that takes your exception type, by reference, and returns a string. It can appear anywhere in the code - it doesn't have to be in the same translation unit. For example:
```
CATCH_TRANSLATE_EXCEPTION( MyType& ex ) {
return ex.message();
}
```
---
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