# fn() lexicalCast
Interpret the character sequence in `source` as the numeric value and write to `target`.

Defined in | <seqan/stream.h>
Signature | `bool lexicalCast(target, source); TTarget lexicalCast<TTarge>(source) // throws BadLexicalCast`

## Parameters

`target` | A numeric value to write to.
`source` | The source sequence of `char` to convert.

## Template Parameters

`TTarget` | The type to use for lexical cast of `source`.

## Return Values

`bool` | `true` if successful and `false` if there was a problem with the cast.

## Detailed Description

### Examples

The following example shows some lexical cast from various sequence types to numbers.

    #include <iostream>
    #include <string>

    #include <seqan/sequence.h>
    #include <seqan/stream.h>

    using namespace seqan;

    int main()
    {
        // interpret string literal as int
        int x = 0;
        // successful cast
        std::cout << "success=" << lexicalCast(x, "123") << ", x=" << x << "\n";
        // unsuccessful cast
        std::cout << "success=" << lexicalCast(x, "42a") << ", x=" << x << "\n";

        // interpret std::string as int
        std::cout << "success=" << lexicalCast(x, std::string("234")) << ", x=" << x << "\n";
        // interpret CharString as int
        std::cout << "success=" << lexicalCast(x, CharString("345")) << ", x=" << x << "\n";
        // interpret infix as int
        CharString str = "123";
        std::cout << "success=" << lexicalCast(x, infix(str, 1, 2)) << ", x=" << x << "\n";

        // interpret literal as float and double
        float f = -1;
        double d = -1;
        std::cout << "success=" << lexicalCast(f, "3.1") << ", f=" << f << "\n"
                  << "success=" << lexicalCast(d, "4.2") << ", d=" << d << "\n";

        // demonstrate throwing of exceptions with lexicalCast()
        try
        {
            x = lexicalCast<int>("a");
        }
        catch (BadLexicalCast const & badCast)
        {
            std::cout << "error: " << badCast.what() << "\n";
        }

        // demonstrate throwing of exceptions with lexicalCastWithException
        try
        {
            lexicalCastWithException(x, "b");
        }
        catch (BadLexicalCast const & badCast)
        {
            std::cout << "error: " << badCast.what() << "\n";
        }

        return 0;
    }

Demo: demos/dox/stream/lexical_cast.cpp

    success=1, x=123
    success=0, x=123
    success=1, x=234
    success=1, x=345
    success=1, x=2
    success=1, f=3.1
    success=1, d=4.2
    error: Unable to convert 'a' into int.
    error: Unable to convert 'b' into int.

## Thrown Exceptions

`BadLexicalCast` | The second variant throws BadLexicalCast in the case that casting failed.

## Data Races

Thread safety unknown!

#### Dox Sources

    /*!
     * @fn lexicalCast
     *
     * @headerfile <seqan/stream.h>
     *
     * @brief Interpret the character sequence in <tt>source</tt> as the numeric
     *        value and write to <tt>target</tt>.
     *
     * @signature bool lexicalCast(target, source);
     * @signature TTarget lexicalCast<TTarge>(source) // throws BadLexicalCast
     *
     * @tparam TTarget The type to use for lexical cast of <tt>source</tt>.
     *
     * @param[out] target A numeric value to write to.
     * @param[in] source The source sequence of <tt>char</tt> to convert.
     *
     * @return bool <tt>true</tt> if successful and <tt>false</tt> if there was a
     *              problem with the cast.
     *
     * @throw BadLexicalCast The second variant throws @link BadLexicalCast @endlink
     *                       in the case that casting failed.
     *
     * @section Examples
     *
     * The following example shows some lexical cast from various sequence types to
     * numbers.
     *
     * @include demos/dox/stream/lexical_cast.cpp
     *
     * @include demos/dox/stream/lexical_cast.cpp.stdout
     */