DCValue Struct Reference

Run time information data type. More...

#include <devlib_types.h>

Inheritance diagram for DCValue:

Data Fields
PropertyType	type
	Value Type.
size_t	len
	length of array, if buffer type
uint16_t	flags
	Public Flags.
long	i
	Union: Integer value.
float	f
	Union: Float value.
void *	p
	Union: Generic Pointer value.

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Detailed Description

This contains a value union and a type field

A DCValue is to be initialized as follows:

 v.type = <type>; v.value.<valuefield> = <value> 

For example, see macros SET_FLOAT, etc.

In case of a string or buffer value, it is important to know that the data buffer is not owned by the property structure, i.e. the DCValue only serves as a descriptor and no value copying actually happens. Therefore, the programmer has to distinguish between two cases before querying a property via dcDevice_GetProperty()

• The property is locally static, i.e. lives on the client's heap: The caller does not have to worry about pointer initialization of the DCValue before calling dcDevice_GetProperty()
• The property is dynamic (read/write) and the caller *must* initialize the value buffer.

If in doubt, ALWAYS initialize a string buffer. If value.p was changed within the call, you can release the buffer and assume that the property is static.

For a dynamic string, the initialization would look as follows:

#define BUF_LEN 80
        DCValue v;
        char buffer[BUF_LEN];
        v.type = DC_STRING; v.len = BUF_LEN; v.value.p = buffer;

        dcDevice_GetProperty(d, property, &v);
        // ...
        //

Note that in this example, the (zero terminated) string has a maximum length of 79.

If there was not enough space reserved for the property buffer, an error DCERR_PROPERTY_SIZE_MATCH is returned from dcGetProperty()

Data type checking is performed when setting properties.

Examples:

handler.c, and master.c.

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The documentation for this struct was generated from the following file:

• devlib_types.h