3.7 Options to Control Diagnostic Messages Formatting
Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...). You can use the
options described below
to control the formatting algorithm for diagnostic messages,
e.g. how many characters per line, how often source location
information should be reported. Note that some language front ends may not
honor these options.
- Try to format error messages so that they fit on lines of about
n characters. If n is zero, then no line-wrapping is
done; each error message appears on a single line. This is the
default for all front ends.
- Only meaningful in line-wrapping mode. Instructs the diagnostic messages
reporter to emit source location information once; that is, in
case the message is too long to fit on a single physical line and has to
be wrapped, the source location won't be emitted (as prefix) again,
over and over, in subsequent continuation lines. This is the default
- Only meaningful in line-wrapping mode. Instructs the diagnostic
messages reporter to emit the same source location information (as
prefix) for physical lines that result from the process of breaking
a message which is too long to fit on a single line.
- Use color in diagnostics. WHEN is ‘never’, ‘always’,
or ‘auto’. The default depends on how the compiler has been configured,
it can be any of the above WHEN options or also ‘never’
if GCC_COLORS environment variable isn't present in the environment,
and ‘auto’ otherwise.
‘auto’ means to use color only when the standard error is a terminal.
The forms -fdiagnostics-color and -fno-diagnostics-color are
aliases for -fdiagnostics-color=always and
The colors are defined by the environment variable GCC_COLORS.
Its value is a colon-separated list of capabilities and Select Graphic
Rendition (SGR) substrings. SGR commands are interpreted by the
terminal or terminal emulator. (See the section in the documentation
of your text terminal for permitted values and their meanings as
character attributes.) These substring values are integers in decimal
representation and can be concatenated with semicolons.
Common values to concatenate include
‘1’ for bold,
‘4’ for underline,
‘5’ for blink,
‘7’ for inverse,
‘39’ for default foreground color,
‘30’ to ‘37’ for foreground colors,
‘90’ to ‘97’ for 16-color mode foreground colors,
‘38;5;0’ to ‘38;5;255’
for 88-color and 256-color modes foreground colors,
‘49’ for default background color,
‘40’ to ‘47’ for background colors,
‘100’ to ‘107’ for 16-color mode background colors,
and ‘48;5;0’ to ‘48;5;255’
for 88-color and 256-color modes background colors.
The default GCC_COLORS is
where ‘01;31’ is bold red, ‘01;35’ is bold magenta,
‘01;36’ is bold cyan, ‘01;32’ is bold green and
‘01’ is bold. Setting GCC_COLORS to the empty
string disables colors.
Supported capabilities are as follows.
- SGR substring for error: markers.
- SGR substring for warning: markers.
- SGR substring for note: markers.
- SGR substring for caret line.
- SGR substring for location information, ‘file:line’ or
- SGR substring for information printed within quotes.
- By default, each diagnostic emitted includes text indicating the
command-line option that directly controls the diagnostic (if such an
option is known to the diagnostic machinery). Specifying the
-fno-diagnostics-show-option flag suppresses that behavior.
- By default, each diagnostic emitted includes the original source line
and a caret ‘^’ indicating the column. This option suppresses this
information. The source line is truncated to n characters, if
the -fmessage-length=n option is given. When the output is done
to the terminal, the width is limited to the width given by the
COLUMNS environment variable or, if not set, to the terminal width.