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Boost.Test > Components > The Test Tools > Output operations testing > boost::test_tools::ostream_test_stream

# boost::test_tools::ostream_test_stream

The class boost::test_tools::ostream_test_stream encapsulates procedures needed for effective and convenient operator<<( std::ostream&, ... ) correctness checks.

## Synopsis

    class output_test_stream {
    pubic:
        explicit  output_test_stream( const_string pattern_file   = const_string(),
                                      bool         match_or_save  = true,
                                      bool         text_or_binary = true );
                  ~output_test_stream();

        bool      is_empty( bool flush_stream = true );
        bool      check_length( std::size_t length, bool flush_stream = true );
        bool      is_equal( const_string arg, bool flush_stream = true );
        bool      match_pattern( bool flush_stream = true );

        void      flush();
    };

### Description

The class output_test_stream models output stream. Formatted output is storred inside of output_test_stream object until check operations are performed at which time the content gets flushed (unless expletely told not to)

### explicit output_test_stream( const_string pattern_file, bool match_or_save, bool text_or_binary )

Effects:

Initilize output test stream object based on arguments provided

Arguments:

pattern_file | - | the pattern file name. If provided file matching/saving operation is permitted. If not only explicit checks on formatted content are permitted
match_or_save | - | boolean switch between matching and saving to pattern file operating modes. Ignored if pattern file name is not supplied
text_or_binary | - | boolean switch between text and binary mode for pattern file reading/writting operations. Ignored if pattern file name is not supplied

### void flush()

Effects:

Clears the content of an output_test_stream object.

### bool is_empty( bool flush_stream )

Effects:

Checks that the content of the output_test_stream instance is empty.

Arguments:

flush_stream | - | boolean flag indicating wheather output_test_strean object content needs to be cleared at the end of the check

Returns:

true if check successful, false otherwise.

### bool check_length( std::size_t length, bool flush_stream )

Effects:

Checks that the length of the output_test_stream object content is equal to supplied length value.

Arguments:

length | - | length value to be matched against
flush_stream | - | boolean flag indicating wheather output_test_strean object content needs to be cleared at the end of the check

Returns:

true if check successful, false otherwise.

### bool is_equal( const_string arg, bool flush_stream )

Effects:

Checks that the content of the output_test_stream instance match the supplied string.

Arguments:

arg | - | character string to be matched against
flush_stream | - | boolean flag indicating wheather output_test_strean object content needs to be cleared at the end of the check

Returns:

true if check successful, false otherwise.

### bool match_pattern( bool flush_stream )

Effects:

Matches the content of the output_test_stream instance versus the pattern file. The pattern file name is specified in the class output_test_stream constructor. If second argument of the class output_test_stream constructor is false, then every call of this method causes the output_test_stream object content to be stored at the end of the pattern file.

Arguments:

flush_stream | - | boolean flag indicating wheather output_test_strean object content needs to be cleared at the end of the check

Returns:

In matching mode: true if check successful, false otherwise. In saving mode always true