FMTMSG(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
fmtmsg — display a message in the specified format on standard error and/or a system console

SYNOPSIS

#include <fmtmsg.h>

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

DESCRIPTION
The fmtmsg() function shall display messages in a specified format instead of the traditional printf() function.

Based on a message's classification component, fmtmsg() shall write a formatted message either to standard error, to the console, or to both.

A formatted message consists of up to five components as defined below. The component classification is not part of a message displayed to the user, but defines the source of the message and directs the display of the formatted message.

classification
    Contains the sum of identifying values constructed from the constants defined below. Any one identifier from a subclass may be used in combination with a single identifier from a different subclass. Two or more identifiers from the same subclass should not be used together, with the exception of identifiers from the display subclass. (Both display subclass identifiers may be used so that messages can be displayed to both standard error and the system console.)

    Major Classifications
        Identifies the source of the condition. Identifiers are: MM_HARD (hardware), MM_SOFT (software), and MM_FIRM (firmware).

    Message Source Subclassifications
        Identifies the type of software in which the problem is detected. Identifiers are: MM_APPL (application), MM_UTIL (utility), and MM_OPSYS (operating system).

    Display Subclassifications
        Indicates where the message is to be displayed. Identifiers are: MM_PRINT to display the message on the standard error stream, MM_CONSOLE to display the message on the system console. One or both identifiers may be used.

    Status Subclassifications
        Indicates whether the application can recover from the condition. Identifiers are: MM_RECOVER (recoverable) and MM_NRECOV (non-recoverable).

    An additional identifier, MM_NULLMC, indicates that no classification component is supplied for the message.

label
    Identifies the source of the message. The format is two fields separated by a <colon>. The first field is up to 10 bytes, the second is up to 14 bytes.

severity
    Indicates the seriousness of the condition. Identifiers for the levels of severity are:

    MM_HALT
        Indicates that the application has encountered a severe fault and is halting. Produces the string "HALT".

    MM_ERROR
        Indicates that the application has detected a fault. Produces the string "ERROR".

    MM_WARNING
        Indicates a condition that is out of the ordinary, that might be a problem, and should be watched. Produces the string "WARNING".

    MM_INFO
        Provides information about a condition that is not in error. Produces the string "INFO".

    MM_NOSEV
        Indicates that no severity level is supplied for the message.

text
    Describes the error condition that produced the message. The character string is not limited to a specific size. If the character string is empty, then the text produced is unspecified.

action
    Describes the first step to be taken in the error-recovery process. The fmtmsg() function precedes the action string with the prefix: "TOFIX:". The action string is not limited to a specific size.

tag An identifier that references on-line documentation for the message. Suggested usage is that tag includes the label and a unique identifying number. A sample tag is "XSI:cat:146".

The MSGVERB environment variable (for message verbosity) shall determine for fmtmsg() which message components it is to select when writing messages to standard error. The value of MSGVERB shall be a <colon>-separated list of optional keywords. Valid keywords are: label, severity, text, action, and tag. If MSGVERB contains a keyword for a component and the component's value is not the component's null value, fmtmsg() shall include that component in the message when writing the message to standard error. If MSGVERB does not include a keyword for a message component, that component shall not be included in the display of the message. The keywords may appear in any order. If MSGVERB is not defined, if its value is the null string, if its value is not of the correct format, or if it contains keywords other than the valid ones listed above, fmtmsg() shall select all components.

MSGVERB shall determine which components are selected for display to standard error. All message components shall be included in console messages.

RETURN VALUE
The fmtmsg() function shall return one of the following values:

MM_OK
    The function succeeded.

MM_NOTOK
    The function failed completely.

MM_NOMSG
    The function was unable to generate a message on standard error, but otherwise succeeded.

MM_NOCON
    The function was unable to generate a console message, but otherwise succeeded.

ERRORS
None.

The following sections are informative.

EXAMPLES

1.  The following example of fmtmsg():

        fmtmsg(MM_PRINT, "XSI:cat", MM_ERROR, "illegal option",
        "refer to cat in user's reference manual", "XSI:cat:001")

    produces a complete message in the specified message format:

        XSI:cat: ERROR: illegal option
        TO FIX: refer to cat in user's reference manual XSI:cat:001

2.  When the environment variable MSGVERB is set as follows:

        MSGVERB=severity:text:action

    and Example 1 is used, fmtmsg() produces:

        ERROR: illegal option
        TO FIX: refer to cat in user's reference manual

APPLICATION USAGE
One or more message components may be systematically omitted from messages generated by an application by using the null value of the argument for that component.

RATIONALE
None.

FUTURE DIRECTIONS
None.

SEE ALSO
fprintf()

The Base Definitions volume of POSIX.1-2017, <fmtmsg.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .