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66 lines
2.4 KiB
Markdown
66 lines
2.4 KiB
Markdown
<a id="top"></a>
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# String conversions
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Catch needs to be able to convert types you use in assertions and logging expressions into strings (for logging and reporting purposes).
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Most built-in or std types are supported out of the box but there are two ways that you can tell Catch how to convert your own types (or other, third-party types) into strings.
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## operator << overload for std::ostream
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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:
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```
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std::ostream& operator << ( std::ostream& os, T const& value ) {
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os << convertMyTypeToString( value );
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return os;
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}
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```
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(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).
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You should put this function in the same namespace as your type and have it declared before including Catch's header.
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## Catch::StringMaker<T> specialisation
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If you don't want to provide an ```operator <<``` overload, or you want to convert your type differently for testing purposes, you can provide a specialization for `Catch::StringMaker<T>`:
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```
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namespace Catch {
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template<>
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struct StringMaker<T> {
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static std::string convert( T const& value ) {
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return convertMyTypeToString( value );
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}
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};
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}
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```
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## Catch::is_range<T> specialisation
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As a fallback, Catch attempts to detect if the type can be iterated
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(`begin(T)` and `end(T)` are valid) and if it can be, it is stringified
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as a range. For certain types this can lead to infinite recursion, so
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it can be disabled by specializing `Catch::is_range` like so:
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```cpp
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namespace Catch {
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template<>
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struct is_range<T> {
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static const bool value = false;
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};
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}
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```
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## Exceptions
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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:
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```
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CATCH_TRANSLATE_EXCEPTION( MyType& ex ) {
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return ex.message();
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}
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```
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---
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[Home](Readme.md#top)
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