pragma Warnings (On | Off);
pragma Warnings (On | Off, LOCAL_NAME);
pragma Warnings (static_string_EXPRESSION);
pragma Warnings (On | Off, static_string_EXPRESSION);
Normally warnings are enabled, with the output being controlled by
the command line switch. Warnings (Off) turns off generation of
warnings until a Warnings (On) is encountered or the end of the
current unit. If generation of warnings is turned off using this
pragma, then no warning messages are output, regardless of the
setting of the command line switches.
The form with a single argument may be used as a configuration pragma.
If the LOCAL_NAME parameter is present, warnings are suppressed for
the specified entity. This suppression is effective from the point where
it occurs till the end of the extended scope of the variable (similar to
the scope of Suppress).
The form with a single static_string_EXPRESSION argument provides more precise control over which warnings are active. The string is a list of letters specifying which warnings are to be activated and which deactivated. The code for these letters is the same as the string used in the command line switch controlling warnings. For a brief summary, use the gnatmake command with no arguments, which will generate usage information containing the list of warnings switches supported. For full details see Warning Message Control.
The warnings controlled by the `-gnatw' switch are generated by the front end of the compiler. The `GCC' back end can provide additional warnings and they are controlled by the `-W' switch. The form with a single static_string_EXPRESSION argument also works for the latters, but the string must be a single full `-W' switch in this case. The above reference lists a few examples of these additional warnings.
The specified warnings will be in effect until the end of the program or another pragma Warnings is encountered. The effect of the pragma is cumulative. Initially the set of warnings is the standard default set as possibly modified by compiler switches. Then each pragma Warning modifies this set of warnings as specified. This form of the pragma may also be used as a configuration pragma.
The fourth form, with an On|Off parameter and a string, is used to
control individual messages, based on their text. The string argument
is a pattern that is used to match against the text of individual
warning messages (not including the initial "warning: " tag).
The pattern may contain asterisks, which match zero or more characters in
the message. For example, you can use
pragma Warnings (Off, "*bits of*unused") to suppress the warning
message warning: 960 bits of "a" unused. No other regular
expression notations are permitted. All characters other than asterisk in
these three specific cases are treated as literal characters in the match.
The above use of patterns to match the message applies only to warning messages generated by the front end. This form of the pragma with a string argument can also be used to control back end warnings controlled by a "-Wxxx" switch. Such warnings can be identified by the appearence of a string of the form "[-Wxxx]" in the message which identifies the "-W" switch that controls the message. By using the text of the "-W" switch in the pragma, such back end warnings can be turned on and off.
There are two ways to use the pragma in this form. The OFF form can be used as a configuration pragma. The effect is to suppress all warnings (if any) that match the pattern string throughout the compilation (or match the -W switch in the back end case).
The second usage is to suppress a warning locally, and in this case, two pragmas must appear in sequence:
pragma Warnings (Off, Pattern);
... code where given warning is to be suppressed
pragma Warnings (On, Pattern);
In this usage, the pattern string must match in the Off and On pragmas, and at least one matching warning must be suppressed.
Note: to write a string that will match any warning, use the string
"***". It will not work to use a single asterisk or two asterisks
since this looks like an operator name. This form with three asterisks
is similar in effect to specifying pragma Warnings (Off) except that a
matching pragma Warnings (On, "***") will be required. This can be
helpful in avoiding forgetting to turn warnings back on.
Note: the debug flag -gnatd.i (/NOWARNINGS_PRAGMAS in VMS) can be
used to cause the compiler to entirely ignore all WARNINGS pragmas. This can
be useful in checking whether obsolete pragmas in existing programs are hiding
real problems.
Note: pragma Warnings does not affect the processing of style messages. See separate entry for pragma Style_Checks for control of style messages.