doc/html_generated/stringification.html - github/onqtam/doctest - Gitiles

 <!DOCTYPE html>
 <html>
 <title>stringification</title>
 <xmp theme="united" style="display:none;">

 ## String conversions

 **doctest** needs to be able to convert types you use in assertions and logging expressions into strings (for logging and reporting purposes).
 Most built-in types are supported out of the box but there are three ways that you can tell **doctest** how to convert your own types (or other, third-party types) into strings.

 For stringifying enums checkout [this issue](https://github.com/onqtam/doctest/issues/121).

 ## ```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, const T& 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;
 }
 ```

 ## ```doctest::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 ```toString()``` for your type which returns ```doctest::String```.

 ```
 namespace user {
     struct udt {};

     doctest::String toString(const udt& value) {
         return convertMyTypeToString(value);
     }
 }
 ```

 Note that the function must be in the same namespace as your type. If the type is not in any namespace - then the overload should be in the global namespace as well. ```convertMyTypeToString``` is where you'll write whatever code is necessary to make your type printable.

 ## ```doctest::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 doctest {
     template<> struct StringMaker<T> {
         static String convert(const T& value) {
             return convertMyTypeToString(value);
         }
     };
 }
 ```

 ## Translating exceptions

 By default all exceptions deriving from ```std::exception``` will be translated to strings by calling the ```what()``` method (also C strings). For exception types that do not derive from ```std::exception``` - or if ```what()``` does not return a suitable string - use ```REGISTER_EXCEPTION_TRANSLATOR```. This defines a function that takes your exception type and returns a ```doctest::String```. It can appear anywhere in the code - it doesn't have to be in the same translation unit. For example:

 ```
 REGISTER_EXCEPTION_TRANSLATOR(MyType& ex) {
     return doctest::String(ex.message());
 }
 ```

 Note that the exception may be accepted without a reference but it is considered bad practice in C++.

 An alternative way to register an exception translator is to do the following in some function - before executing any tests:

 ```
     // adding a lambda - the signature required is `doctest::String(exception_type)`
     doctest::registerExceptionTranslator<int>([](int in){ return doctest::toString(in); });
 ```

 The order of registering exception translators can be controlled - simply call the explicit function in the required order or list the exception translators with the macro in a top-to-bottom fashion in a single translation unit - everything that auto-registers in doctest works in a top-to-bottom way for a single translation unit (source file).

 ------

 - Check out the [**example**](../../examples/all_features/stringification.cpp) which shows how to stringify ```std::vector<T>``` and other types/exceptions.
 - Note that the type ```String``` is used when specializing ```StringMaker<T>``` or overloading ```toString()``` - it is the string type **doctest** works with. ```std::string``` is not an option because doctest would have to include the ```<string>``` header.
 - To support the ```operator<<(std::ostream&...``` stringification the library has to offer a forward declaration of ```std::ostream``` and that is what the library does - but it is forbidden by the standard. It currently works everywhere - on all tested compilers - but if the user wishes to be 100% standards compliant - then the [**```DOCTEST_CONFIG_USE_IOSFWD```**](configuration.html#doctest_config_use_iosfwd) identifier can be used to force the inclusion of ```<iosfwd>```. The reason the header is not included by default is that on MSVC (for example) it drags a whole bunch of stuff with it - and after the preprocessor is finished the translation unit has grown to 42k lines of C++ code - while Clang and the libc++ are so well implemented that including ```<iosfwd>``` there results in 400 lines of code.

 ---

 [Home](readme.html#reference)

 <p align="center"><img src="../../scripts/data/logo/icon_2.svg"></p>


 </xmp>
 <script src="strapdown.js/strapdown.js"></script>
 </html>
	<!DOCTYPE html>
	<html>
	<title>stringification</title>
	<xmp theme="united" style="display:none;">

	## String conversions

	doctest needs to be able to convert types you use in assertions and logging expressions into strings (for logging and reporting purposes).
	Most built-in types are supported out of the box but there are three ways that you can tell doctest how to convert your own types (or other, third-party types) into strings.

	For stringifying enums checkout [this issue](https://github.com/onqtam/doctest/issues/121).

	## ```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, const T& 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;
	}
	```

	## ```doctest::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 ```toString()``` for your type which returns ```doctest::String```.

	```
	namespace user {
	struct udt {};

	doctest::String toString(const udt& value) {
	return convertMyTypeToString(value);
	}
	}
	```

	Note that the function must be in the same namespace as your type. If the type is not in any namespace - then the overload should be in the global namespace as well. ```convertMyTypeToString``` is where you'll write whatever code is necessary to make your type printable.

	## ```doctest::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 doctest {
	template<> struct StringMaker<T> {
	static String convert(const T& value) {
	return convertMyTypeToString(value);
	}
	};
	}
	```

	## Translating exceptions

	By default all exceptions deriving from ```std::exception``` will be translated to strings by calling the ```what()``` method (also C strings). For exception types that do not derive from ```std::exception``` - or if ```what()``` does not return a suitable string - use ```REGISTER_EXCEPTION_TRANSLATOR```. This defines a function that takes your exception type and returns a ```doctest::String```. It can appear anywhere in the code - it doesn't have to be in the same translation unit. For example:

	```
	REGISTER_EXCEPTION_TRANSLATOR(MyType& ex) {
	return doctest::String(ex.message());
	}
	```

	Note that the exception may be accepted without a reference but it is considered bad practice in C++.

	An alternative way to register an exception translator is to do the following in some function - before executing any tests:

	```
	// adding a lambda - the signature required is `doctest::String(exception_type)`
	doctest::registerExceptionTranslator<int>([](int in){ return doctest::toString(in); });
	```

	The order of registering exception translators can be controlled - simply call the explicit function in the required order or list the exception translators with the macro in a top-to-bottom fashion in a single translation unit - everything that auto-registers in doctest works in a top-to-bottom way for a single translation unit (source file).

	------

	- Check out the [example](../../examples/all_features/stringification.cpp) which shows how to stringify ```std::vector<T>``` and other types/exceptions.
	- Note that the type ```String``` is used when specializing ```StringMaker<T>``` or overloading ```toString()``` - it is the string type doctest works with. ```std::string``` is not an option because doctest would have to include the ```<string>``` header.
	- To support the ```operator<<(std::ostream&...``` stringification the library has to offer a forward declaration of ```std::ostream``` and that is what the library does - but it is forbidden by the standard. It currently works everywhere - on all tested compilers - but if the user wishes to be 100% standards compliant - then the [```DOCTEST_CONFIG_USE_IOSFWD```](configuration.html#doctest_config_use_iosfwd) identifier can be used to force the inclusion of ```<iosfwd>```. The reason the header is not included by default is that on MSVC (for example) it drags a whole bunch of stuff with it - and after the preprocessor is finished the translation unit has grown to 42k lines of C++ code - while Clang and the libc++ are so well implemented that including ```<iosfwd>``` there results in 400 lines of code.

	---

	[Home](readme.html#reference)

	<p align="center"><img src="../../scripts/data/logo/icon_2.svg"></p>


	</xmp>
	<script src="strapdown.js/strapdown.js"></script>
	</html>