Originální popis anglicky:
fmtmsg - print formatted error messages
Návod, kniha: Linux Programmer's Manual
#include <fmtmsg.h>
int fmtmsg(long classification, const char *label,
int severity, const char *text,
const char *action, const char *tag);
This function displays a message described by its parameters on the device(s)
specified in the
classification parameter. For messages written to
stderr, the format depends on the
MSGVERB environment variable.
The
label parameter identifies the source of the message. The string must
consist of two colon separated parts where the first part has not more than 10
and the second part not more than 14 characters.
The
text parameter describes the condition of the error.
The
action parameter describes possible steps to recover from the error.
If it is printed, it is prefixed by "TO FIX: ".
The
tag parameter is a reference to the online documentation where more
information can be found. It should contain the
label value and a
unique identification number.
Each of the parameters can have a dummy value. The dummy classification value
MM_NULLMC (0L) does not specify any output, so nothing is printed. The
dummy severity value
NO_SEV (0) says that no severity is supplied. The
values
MM_NULLLBL,
MM_NULLTXT,
MM_NULLACT,
MM_NULLTAG are synonyms for ((char *) 0), the empty string, and
MM_NULLSEV is a synonym for
NO_SEV.
The
classification parameter is the sum of values describing 4 types of
information.
The first value defines the output channel.
- MM_PRINT
- Output to stderr.
- MM_CONSOLE
- Output to the system console.
- MM_PRINT | MM_CONSOLE
- Output to both.
The second value is the source of the error:
- MM_HARD
- A hardware error occurred.
- MM_FIRM
- A firmware error occurred.
- MM_SOFT
- A software error occurred.
The third value encodes the detector of the problem:
- MM_APPL
- It is detected by an application.
- MM_UTIL
- It is detected by a utility.
- MM_OPSYS
- It is detected by the operating system.
The fourth value shows the severity of the incident:
- MM_RECOVER
- It is a recoverable error.
- MM_NRECOV
- It is a non-recoverable error.
The
severity parameter can take one of the following values:
- MM_NOSEV
- No severity is printed.
- MM_HALT
- This value is printed as HALT.
- MM_ERROR
- This value is printed as ERROR.
- MM_WARNING
- This value is printed as WARNING.
- MM_INFO
- This value is printed as INFO.
The numeric values are between 0 and 4. Using
addseverity() or the
environment variable
SEV_LEVEL you can add more levels and strings to
print.
The environment variable
MSGVERB ("message verbosity") can be
used to suppress parts of the output to
stderr. (It does not influence
output to the console.) When this variable is defined, is non-NULL, and is a
colon-separated list of valid keywords, then only the parts of the message
corresponding to these keywords is printed. Valid keywords are
"label", "severity", "text", "action"
and "tag".
The environment variable
SEV_LEVEL can be used to introduce new severity
levels. By default, only the five severity levels described above are
available. Any other numeric value would make fmtmsg() print nothing. If the
user puts
SEV_LEVEL with a format like
SEV_LEVEL=[description[:description[:...]]]
in the environment of the process before the first call to fmtmsg(), where each
description is of the form
severity-keyword,level,printstring
then
fmtmsg() will also accept the indicated values for the level (in
addition to the standard levels 0-4), and use the indicated printstring when
such a level occurs.
The severity-keyword part is not used by
fmtmsg() but it has to be
present. The level part is a string representation of a number. The numeric
value must be a number greater than 4. This value must be used in the severity
parameter of
fmtmsg() to select this class. It is not possible to
overwrite any of the predefined classes. The printstring is the string printed
when a message of this class is processed by
fmtmsg().
The function can return 4 values:
- MM_OK
- Everything went smooth.
- MM_NOTOK
- Complete failure.
- MM_NOMSG
- Error writing to stderr.
- MM_NOCON
- Error writing to the console.
The functions
fmtmsg() and
addseverity(), and environment
variables
MSGVERB and
SEV_LEVEL come from System V (XPG4-UNIX).
The function
fmtmsg() and the environment variable
MSGVERB are
described in POSIX 1003.1-2001.
System V and Unixware man pages tell us that these functions have been replaced
by "pfmt() and addsev()" or by "pfmt(), vpfmt(), lfmt(), and
vlfmt()", and will be removed later.
#include <stdio.h>
#include <fmtmsg.h>
int main() {
long class = MM_PRINT | MM_SOFT | MM_OPSYS | MM_RECOVER;
int err;
err = fmtmsg(class, "util-linux:mount", MM_ERROR,
"unknown mount option", "See mount(8).", "util-linux:mount:017");
switch(err) {
case MM_OK:
break;
case MM_NOTOK:
printf("Nothing printed\n");
break;
case MM_NOMSG:
printf("Nothing printed to stderr\n");
break;
case MM_NOCON:
printf("No console output\n");
break;
default:
printf("Unknown error from fmtmsg()\n");
}
return 0;
}
The output should be:
util-linux:mount: ERROR: unknown mount option
TO FIX: See mount(8). util-linux:mount:017
and after
MSGVERB=text:action; export MSGVERB
the output becomes:
unknown mount option
TO FIX: See mount(8).
addseverity(3),
perror(3)
