Some binary file formats use variable types that are different from the regular Data Types. 010 Editor has a powerful syntax for letting you define custom variables in practically any format. To build a custom variable, write a custom function that converts a variable into a string. This string will be displayed in the Template Results panel as the value for the variable (this custom function is called a read function). Optionally, a write function can be written that converts a string in the Template Results panel back to the variable when the variable is edited and Enter is pressed. To assign a read and write function to a variable, use the syntax '<read= <function name> [, write= <function name> ] >'after a typedef. A read function takes as arguments a variable and returns a string. A write function takes as arguments a reference to a variable and a string. For example, to define a fixed point data type that uses 16 bits (the 8 high bits define the whole part and the 8 low bits define the fractional part), use:

    typedef ushort FIXEDPT <read=FIXEDPTRead, write=FIXEDPTWrite>;

    string FIXEDPTRead( FIXEDPT f )
    {
        string s;   
        SPrintf( s, "%lg", f / 256.0 );
        return s;
    }

    void FIXEDPTWrite( FIXEDPT &f, string s )
    {
        f = (FIXEDPT)( Atof( s ) * 256 );
    }

In this example, the FIXEDPT variable could be defined without a write function using '<read=FIXEDPTRead>', but the variable will be read-only in the Template Results panel. Note that the typedef must be defined before the functions in the source file. If an error can occur when a write function is called, change the return value to int and return 0 on success or -1 on failure.

When displaying arrays in the Template Results panel, usually no value is displayed for an array until the array is opened up. To specify a value beside the array, a custom variable can be defined. For example:

    typedef float VEC3F[3] <read=Vec3FRead, write=Vec3FWrite>;

    string Vec3FRead( VEC3F v )
    {
        string s;   
        SPrintf( s, "(%f %f %f)", v[0], v[1], v[2] );
        return s;
    }

    void Vec3FWrite( VEC3F &v, string s )
    {
        SScanf( s, "(%f %f %f)", v[0], v[1], v[2] );
    }

Note that currently, read/write functions cannot be declared simultaneously for an array of elements and for each element of the array. The same process can be used to display a value for a struct in the Template Results panel. For an example, see the 'ZIPTemplate.bt' file that uses a read function to display the file name beside each structure.