man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

fmtmsg(3C)

Name

fmtmsg - display a message on stderr or 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 writes a formatted message to stderr, to the console, or to both, on a message's classification component. It can be used instead of the traditional printf(3C) interface to display messages to stderr, and in conjunction with gettxt(3C), provides a simple interface for producing language-independent applications.

A formatted message consists of up to five standard components ( label, severity, text, action, and tag) as described below. The classification component is not part of the standard message displayed to the user, but rather defines the source of the message and directs the display of the formatted message.

classification

Contains identifiers from the following groups of major classifications and subclassifications. Any one identifier from a subclass may be used in combination by ORing the values together 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 stderr and the system console).

  • “Major classifications” identify the source of the condition. Identifiers are: MM_HARD (hardware), MM_SOFT (software), and MM_FIRM (firmware).

  • “Message source subclassifications” identify the type of software in which the problem is spotted. Identifiers are: MM_APPL (application), MM_UTIL (utility), and MM_OPSYS (operating system).

  • “Display subclassifications” indicate 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. Neither, either, or both identifiers may be used.

  • “Status subclassifications” indicate whether the application will 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 of this component is two fields separated by a colon. The first field is up to 10 characters long; the second is up to 14 characters. Suggested usage is that label identifies the package in which the application resides as well as the program or application name. For example, the label UX:cat indicates the UNIX System V package and the cat(1) utility.

severity

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

  • MM_HALT indicates that the application has encountered a severe fault and is halting. Produces the print string HALT.

  • MM_ERROR indicates that the application has detected a fault. Produces the print string ERROR.

  • MM_WARNING indicates a condition out of the ordinary that might be a problem and should be watched. Produces the print string WARNING.

  • MM_INFO provides information about a condition that is not in error. Produces the print string INFO.

  • MM_NOSEV indicates that no severity level is supplied for the message.

Other severity levels may be added by using the addseverity() routine.

text

Describes the condition that produced the message. The text string is not limited to a specific size.

action

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

tag

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

Environment Variables

The MSGVERB and SEV_LEVEL environment variables control the behavior of fmtmsg() as follows:

MSGVERB

This variable determines which message components fmtmsg() selects when writing messages to stderr. Its value is a colon-separated list of optional keywords and can be set as follows:

MSGVERB=[keyword[:keyword[: . . .]]]
export MSGVERB

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() includes that component in the message when writing the message to stderr. If MSGVERB does not include a keyword for a message component, that component is not 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() selects all components.

The first time fmtmsg() is called, it examines MSGVERB to determine which message components are to be selected when generating a message to write to the standard error stream, stderr. The values accepted on the initial call are saved for future calls.

The MSGVERB environment variable affects only those components that are selected for display to the standard error stream. All message components are included in console messages.

SEV_LEVEL

This variable defines severity levels and associates print strings with them for use by fmtmsg(). The standard severity levels listed below cannot be modified. Additional severity levels can also be defined, redefined, and removed using addseverity() (see addseverity(3C)). If the same severity level is defined by both SEV_LEVEL and addseverity(), the definition by addseverity () takes precedence.

0

(no severity is used)

1

HALT

2

ERROR

3

WARNING

4

INFO

The SEV_LEVEL variable can be set as follows:

SEV_LEVEL=[description[:description[: . . .]]]
export SEV_LEVEL

where description is a comma-separated list containing three fields:

description=severity_keyword,level,printstring

The severity_keyword field is a character string that is used as the keyword on the –s severity option to the fmtmsg (1) utility. (This field is not used by the fmtmsg() function.)

The level field is a character string that evaluates to a positive integer (other than 0, 1, 2, 3, or 4, which are reserved for the standard severity levels). If the keyword severity_keyword is used, level is the severity value passed on to the fmtmsg() function.

The printstring field is the character string used by fmtmsg() in the standard message format whenever the severity value level is used.

If a description in the colon list is not a three-field comma list, or if the second field of a comma list does not evaluate to a positive integer, that description in the colon list is ignored.

The first time fmtmsg() is called, it examines the SEV_LEVEL environment variable, if defined, to determine whether the environment expands the levels of severity beyond the five standard levels and those defined using addseverity(). The values accepted on the initial call are saved for future calls.

Use in Applications

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.

The table below indicates the null values and identifiers for fmtmsg() arguments.

Argument
Type
Null-Value
Identifier
label
char*
(char*) NULL
MM_NULLLBL
severity
int
0
MM_NULLSEV
class
long
0L
MM_NULLMC
text
char*
(char*) NULL
MM_NULLTXT
action
char*
(char*) NULL
MM_NULLACT
tag
char*
(char*) NULL
MM_NULLTAG

Another means of systematically omitting a component is by omitting the component keyword(s) when defining the MSGVERB environment variable (see the Environment Variables section above).

Return Values

The fmtmsg() returns 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 the standard error stream, but otherwise succeeded.

MM_NOCON

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

Examples

Example 1 The following example of fmtmsg():
fmtmsg(MM_PRINT, "UX:cat", MM_ERROR, "invalid syntax",
"refer to manual", "UX:cat:001")

produces a complete message in the standard message format:

UX:cat: ERROR: invalid syntax
TO FIX: refer to manual   UX:cat:001
Example 2 When the environment variable MSGVERB is set as follows:
MSGVERB=severity:text:action

and the Example 1 is used, fmtmsg() produces:

ERROR: invalid syntax
TO FIX: refer to manual
Example 3 When the environment variable SEV_LEVEL is set as follows:
SEV_LEVEL=note,5,NOTE

the following call to fmtmsg()

fmtmsg(MM_UTIL | MM_PRINT, "UX:cat", 5, "invalid syntax",
"refer to manual", "UX:cat:001")

produces

UX:cat: NOTE: invalid syntax
TO FIX: refer to manual   UX:cat:001

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
Safe
Standard

See Also

fmtmsg(1), addseverity(3C), gettxt(3C), printf(3C), attributes(5), standards(5)