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Manual Reference Pages  -  MSGNO (3)


msgno - manage error codes and associated messages across separate libraries




#include <mba/msgno.h> 

MMSG(fmt, ...) MMNO(msgno) MMNF(msgno, fmt, ...)

/* Primary */ PMSG(fmt, ...) PMNO(msgno) PMNF(msgno, fmt, ...)

/* Additional */ AMSG(fmt, ...) AMNO(msgno) AMNF(msgno, fmt, ...)

extern int (*msgno_hdlr)(const char *fmt, ...);

struct msgno_entry { unsigned int msgno; const char *msg; };

int msgno_add_codes(struct msgno_entry *list);
const char *msgno_msg(unsigned int msgno);
int msgno_hdlr_stderr(const char *fmt,...);


The msgno(3m) module provides a set of macros that when used consistently will generate stacktrace-like output like the following example:

src/expatls.c:97:utf8tods: Character encoding error src/expatls.c:449:start_fn: src/dom.c:405:DOM_Element_normalize: dump.c:30:main: Failed to process sample.xml

Note: As of version 0.9, this implementation no longer uses variadic macros -- it is strict standard C.

Additionally this module provides functions for managing error codes (or more generically message numbers) and associated messages across separate C libraries. This functionality is very similar to the com_err library but with runtime message registration. Each participating library registers a table of messages at runtime with the msgno_add_codes function. The msgno(3m) macros are provided to dispatch messages (e.g. print to stderr).

Note: The msgno(3m) macros operate on a shared buffer and therefore they are not reentrant. Meaning they cannot not be used concurrently by multiple threads.

  The mnsgo_add_codes function registers an array of msgno_entry structures. The array must contain at least one element and the msg member of the last element must be NULL. Each msgno value must be greater than the previous value. Values will be created at runtime if not provided (e.g. all 0s becomes 0,1,2,3,..). Create macros for each message value by referencing the msgno member like the following:

#define DOM_INDEX_SIZE_ERR dom_codes[0].msgno #define DOM_DOMSTRING_SIZE_ERR dom_codes[1].msgno

struct msgno_entry dom_codes[] = { { 1, "The index specified was out of range" }, { 0, "The text size is out of range" }, ... { 0, NULL } };

msg The msgno_msg function returns the message associated with the msgno parameters that have previously been registered with msgno_add_codes. If no such message has been registered, then the message "No such msgno list" or "No such message in msgno list" is returned.
  The msgno_hdlr_stderr function writes msgno messages to stderr. It is the default msgno message handler. The msgno message handler may be changed by reassigning a new function that matches the signature to the msgno_hdlr function pointer.

Tip: If you are working on a Microsoft Windows MFC application, create a msgno_hdlr function like the one below that calls AfxMessageBox and set it to msgno_hdlr in InitInstance. This will permit your MFC application to report errors generated from within libmba.

static int MessageBoxHdlr(const char *fmt, ...) {     char mbs[4096];     wchar_t wcs[4096];     va_list ap;     va_start(ap, fmt);

    _vsnprintf(mbs, 4096, fmt, ap);     if (mbstowcs(wcs, mbs, 4096) != (size_t)-1) {                    AfxMessageBox(wcs);     }

    va_end(ap);     return 0; } BOOL CWutApp::InitInstance() {     ...     msgno_hdlr = MessageBoxHdlr;


  The msgno_add_codes function returns 0 if the operation was successful. Otherwise -1 is returned and errno is set appropriately.
  The msgno_hdlr_stderr function (i.e. the msgno_hdlr function) returns the number of characters printed to stderr.
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libmba-0.9.1 MSGNO (3m) Apr 29, 2005

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