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/*
* Standardized error code module.
* Header file
* ---------------------------------------------------------------------------
* DESIGN
*
* The purpose of this module is to unify error codes and error messages.
*
* Traditionally, errors are assigned an arbitrary integer value (or possibly
* an enumerated value). These codes are unique only within the module that
* defines them; when error codes are returned from several different modules
* it is difficult to distinguish which error came from where. Also, if the
* error code needs to be propagated through several modules, a series of
* conversions are required. To obtain a human-readable message, a special
* error-to-message mapping function is usually needed. After the error code
* has been converted several times, it is difficult to know which mapping
* function should be used.
*
* This module tries to fix these problems. Error codes are defined such that
* every error is unique throughout the entire program. Furthermore, an error
* code equals the error message, and thus the message can be accessed directly
* without any need of locating and using the correct mapping function.
*
* This is accomplished by defining an error code to be a pointer to the
* message describing the error. Since all strings are stored at unique memory
* locations, all error codes will be unique. There is not even a need to
* manually assign unique error codes across all modules (which is impractical,
* especially if library modules are used). Also, the error code itself is
* the pointer to the error message: the message associated with the error is
* right at your fingertips ready to be accessed.
*
* IMPLEMENTATION
*
* By convention, all error codes will have uppercase names, with the first
* part of the name containing a prefix that identifies which module the
* error is defined in. Errors are defined using the 'error_d' typedef:
* error_d STK_CANNOT_POP="Nothing to pop from stack";
* Error codes are stored in variables of type 'error_t', but assigned an
* initial value from 'error_d':
* error_t e;
* e = STK_CANNOT_POP;
* printf("Error: %s\n", e);
*
* By convention, error codes should be declared in the header file of the
* module it belongs to, but defined in the implementation files. So, the
* header file should contain something like:
* extern error_d STK_CANNOT_POP;
* extern error_d STK_INTERNAL_ERROR;
* ... etc.
*/
#ifndef ERROR_H
#define ERROR_H
typedef char error_d[];
typedef char *error_t;
#define NO_ERROR ((error_t)0)
#endif /* ERROR_H */
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