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The header file ‘fterrors.h’ (which is automatically included by ‘freetype.h’ defines the handling of FreeType's enumeration constants. It can also be used to generate error message strings with a small macro trick explained below.
Error Formats
The configuration macro FT_CONFIG_OPTION_USE_MODULE_ERRORS can be defined in ‘ftoption.h’ in order to make the higher byte indicate the module where the error has happened (this is not compatible with standard builds of FreeType 2, however). See the file ‘ftmoderr.h’ for more details.
Error Message Strings
Error definitions are set up with special macros that allow client applications to build a table of error message strings. The strings are not included in a normal build of FreeType 2 to save space (most client applications do not use them).
To do so, you have to define the following macros before including this file.
FT_ERROR_START_LIST
This macro is called before anything else to define the start of the error list. It is followed by several FT_ERROR_DEF calls.
FT_ERROR_DEF( e, v, s )
This macro is called to define one single error. ‘e’ is the error code identifier (e.g., ‘Invalid_Argument’), ‘v’ is the error's numerical value, and ‘s’ is the corresponding error string.
FT_ERROR_END_LIST
This macro ends the list.
Additionally, you have to undefine ‘__FTERRORS_H__’ before #including this file.
Here is a simple example.
#undef __FTERRORS_H__
#define FT_ERRORDEF( e, v, s ) { e, s },
#define FT_ERROR_START_LIST {
#define FT_ERROR_END_LIST { 0, NULL } };
const struct
{
int err_code;
const char* err_msg;
} ft_errors[] =
#include FT_ERRORS_H
Note that ‘FT_Err_Ok’ is not defined with ‘FT_ERRORDEF’ but with ‘FT_NOERRORDEF’; it is always zero.