define

Description

Normally the configuration system generates a single #define for each option that is active and enabled, with the defined symbol being the name of the option. These #define's go to the package's own configuration header file, for example pkgconf/kernel.h for kernel configuration options. For the majority of options this is sufficient. Sometimes it is useful to have more control over which #define's get generated.

The define property can be used to generate an additional #define if the option is both active and enabled, for example:

cdl_option CYGNUM_LIBC_STDIO_FOPEN_MAX {
    …
    define FOPEN_MAX
}

If this option is given the value 40 then the following #define's will be generated in the configuration header pkgconf/libc.h:

#define CYGNUM_LIBC_STDIO_FOPEN_MAX 40
#define FOPEN_MAX 40

The default #define can be suppressed if desired using the no_define property. This is useful if the symbol should only be defined in pkgconf/system.h and not in the package's own configuration header file. The value that will be used for this #define is the same as for the default one, and depends on the option's flavor as follows:

For active options with the data flavor, and for active and enabled options with the booldata flavor, either one or two #define's will be generated. These take the following forms:

#define <symbol> <value>
#define <symbol>_<value>

For the first #define it is possible to control the format used for the value using a -format=<format> option. For example, the following can be used to output some configuration data as a C string:

cdl_option <name> {
    …
    define -format="\\\"%s\\\"" <symbol>
}

The implementation of this facility involves concatenating the Tcl command format, the format string, and the string representation of the option's value, and evaluating this in a Tcl interpreter. Therefore the format string will be processed twice by a Tcl parser, and appropriate care has to be taken with quoting.

The second #define will be generated only if is a valid C preprocessor macro symbol. By default the symbols generated by define properties will end up in the package's own configuration header file. The -file option can be used to specify an alternative destination. At the time of writing the only valid alternative definition is -file=system.h, which will send the output to the global configuration header file pkgconf/system.h.

Example

cdl_component CYG_HAL_STARTUP {
    display       "Startup type"
    flavor        data
    legal_values  {"RAM" "ROM" }
    default_value {"RAM"}
    no_define
    define -file=system.h CYG_HAL_STARTUP
    …
}

See Also

Properties define_format, define_header, define_proc, if_define and no_define.