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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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FMTMSG(3P) POSIX Programmer's Manual FMTMSG(3P)
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.
fmtmsg — display a message in the specified format on standard
error and/or a system console
#include <fmtmsg.h>
int fmtmsg(long classification, const char *label, int severity,
const char *text, const char *action, const char *tag);
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.
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.
None.
The following sections are informative.
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
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.
None.
None.
fprintf(3p)
The Base Definitions volume of POSIX.1‐2017, fmtmsg.h(0p)
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 .
IEEE/The Open Group 2017 FMTMSG(3P)
Pages that refer to this page: fmtmsg.h(0p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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