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FMTMSG(3) Library Functions Manual FMTMSG(3)

fmtmsg — display a detailed diagnostic message

Standard C Library (libc, -lc)

#include <fmtmsg.h>

int
fmtmsg(long classification, const char *label, int severity, const char *text, const char *action, const char *tag);

The () function displays a detailed diagnostic message, based on the supplied arguments, to stderr and/or the system console.

The classification argument is the bitwise inclusive OR of zero or one of the manifest constants from each of the classification groups below. The Output classification group is an exception since both MM_PRINT and MM_CONSOLE may be specified.

Output
Output should take place on stderr.
Output should take place on the system console.
Source of Condition (Major)
The source of the condition is hardware related.
The source of the condition is software related.
The source of the condition is firmware related.
Source of Condition (Minor)
The condition was detected at the application level.
The condition was detected at the utility level.
The condition was detected at the operating system level.
Status
The application can recover from the condition.
The application is unable to recover from the condition.

Alternatively, the MM_NULLMC manifest constant may be used to specify no classification.

The label argument indicates the source of the message. It is made up of two fields separated by a colon (‘:’). The first field can be up to 10 bytes, and the second field can be up to 14 bytes. The MM_NULLLBL manifest constant may be used to specify no label.

The severity argument identifies the importance of the condition. One of the following manifest constants should be used for this argument.

The application has confronted a serious fault and is halting.
The application has detected a fault.
The application has detected an unusual condition, that could be indicative of a problem.
The application is providing information about a non-error condition.
No severity level supplied.

The text argument details the error condition that caused the message. There is no limit on the size of this character string. The MM_NULLTXT manifest constant may be used to specify no text.

The action argument details how the error-recovery process should begin. Upon output, () will prefix "TO FIX:" to the beginning of the action argument. The MM_NULLACT manifest constant may be used to specify no action.

The tag argument should reference online documentation for the message. This usually includes the label and a unique identifying number. An example tag is "BSD:ls:168". The MM_NULLTAG manifest constant may be used to specify no tag.

The fmtmsg() function returns MM_OK upon success, MM_NOMSG to indicate output to stderr failed, MM_NOCON to indicate output to the system console failed, or MM_NOTOK to indicate output to stderr and the system console failed.

The MSGVERB (message verbosity) environment variable specifies which arguments to fmtmsg() will be output to stderr, and in which order. MSGVERB should be a colon (‘:’) separated list of identifiers. Valid identifiers include: label, severity, text, action, and tag. If invalid identifiers are specified or incorrectly separated, the default message verbosity and ordering will be used. The default ordering is equivalent to a MSGVERB with a value of "label:severity:text:action:tag".

The code:

fmtmsg(MM_UTIL | MM_PRINT, "BSD:ls", MM_ERROR,
    "illegal option -- z", "refer to manual", "BSD:ls:001");

will output:

BSD:ls: ERROR: illegal option -- z
TO FIX: refer to manual BSD:ls:001

to stderr.

The same code, with MSGVERB set to "text:severity:action:tag", produces:

illegal option -- z: ERROR
TO FIX: refer to manual BSD:ls:001

err(3), exit(3), strerror(3)

The fmtmsg() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

The fmtmsg() function first appeared in FreeBSD 5.0.

Specifying MM_NULLMC for the classification argument makes little sense, since without an output specified, fmtmsg() is unable to do anything useful.

In order for fmtmsg() to output to the system console, the effective user must have appropriate permission to write to /dev/console. This means that on most systems fmtmsg() will return MM_NOCON unless the effective user is root.

August 5, 2002 macOS