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.
-fmessage-length=
nNote - this option also affects the display of the ‘#error’ and
‘#warning’ pre-processor directives, and the ‘deprecated’
function/type/variable attribute. It does not however affect the
‘pragma GCC warning’ and ‘pragma GCC error’ pragmas.
-fdiagnostics-show-location=once
-fdiagnostics-show-location=every-line
-fdiagnostics-color[=
WHEN]
-fno-diagnostics-color
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
error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ quote=01:fixit-insert=32:fixit-delete=31:\ diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ type-diff=01;32
where ‘01;31’ is bold red, ‘01;35’ is bold magenta, ‘01;36’ is bold cyan, ‘32’ is green, ‘34’ is blue, ‘01’ is bold, and ‘31’ is red. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as follows.
error=
warning=
note=
range1=
range2=
locus=
quote=
fixit-insert=
fixit-delete=
diff-filename=
diff-hunk=
diff-delete=
diff-insert=
type-diff=
-fno-diagnostics-show-option
-fno-diagnostics-show-caret
-fno-diagnostics-show-labels
printf ("foo %s bar", long_i + long_j); ~^ ~~~~~~~~~~~~~~~ | | char * long int
This option suppresses the printing of these labels (in the example above,
the vertical bars and the “char *” and “long int” text).
-fno-diagnostics-show-line-numbers
-fdiagnostics-minimum-margin-width=
width-fdiagnostics-parseable-fixits
fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"
The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for the initial column. In the above example, bytes 3 through 20 of line 45 of “test.c” are to be replaced with the given string:
00000000011111111112222222222 12345678901234567890123456789 gtk_widget_showall (dlg); ^^^^^^^^^^^^^^^^^^ gtk_widget_show_all
The filename and replacement string escape backslash as “\\", tab as “\t”, newline as “\n”, double quotes as “\"”, non-printable characters as octal (e.g. vertical tab as “\013”).
An empty replacement string indicates that the given range is to be removed.
An empty range (e.g. “45:3-45:3”) indicates that the string is to
be inserted at the given position.
-fdiagnostics-generate-patch
--- test.c +++ test.c @ -42,5 +42,5 @ void show_cb(GtkDialog *dlg) { - gtk_widget_showall(dlg); + gtk_widget_show_all(dlg); }
The diff may or may not be colorized, following the same rules
as for diagnostics (see -fdiagnostics-color).
-fdiagnostics-show-template-tree
could not convert 'std::map<int, std::vector<double> >()' from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
the -fdiagnostics-show-template-tree flag enables printing a tree-like structure showing the common and differing parts of the types, such as:
map< [...], vector< [double != float]>>
The parts that differ are highlighted with color (“double” and
“float” in this case).
-fno-elide-type
could not convert 'std::map<int, std::vector<double> >()' from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
Specifying the -fno-elide-type flag suppresses that behavior.
This flag also affects the output of the
-fdiagnostics-show-template-tree flag.
-fno-show-column
-fdiagnostics-format=
FORMATThe ‘json’ format consists of a top-level JSON array containing JSON objects representing the diagnostics.
The JSON is emitted as one line, without formatting; the examples below have been formatted for clarity.
Diagnostics can have child diagnostics. For example, this error and note:
misleading-indentation.c:15:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation] 15 | if (flag) | ^~ misleading-indentation.c:17:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if' 17 | y = 2; | ^
might be printed in JSON form (after formatting) like this:
[ { "kind": "warning", "locations": [ { "caret": { "column": 3, "file": "misleading-indentation.c", "line": 15 }, "finish": { "column": 4, "file": "misleading-indentation.c", "line": 15 } } ], "message": "this \u2018if\u2019 clause does not guard...", "option": "-Wmisleading-indentation", "children": [ { "kind": "note", "locations": [ { "caret": { "column": 5, "file": "misleading-indentation.c", "line": 17 } } ], "message": "...this statement, but the latter is ..." } ] }, ... ]
where the note
is a child of the warning
.
A diagnostic has a kind
. If this is warning
, then there is
an option
key describing the command-line option controlling the
warning.
A diagnostic can contain zero or more locations. Each location has up
to three positions within it: a caret
position and optional
start
and finish
positions. A location can also have
an optional label
string. For example, this error:
bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka 'struct s'} and 'T' {aka 'struct t'}) 64 | return callee_4a () + callee_4b (); | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ | | | | | T {aka struct t} | S {aka struct s}
has three locations. Its primary location is at the “+” token at column 23. It has two secondary locations, describing the left and right-hand sides of the expression, which have labels. It might be printed in JSON form as:
{ "children": [], "kind": "error", "locations": [ { "caret": { "column": 23, "file": "bad-binary-ops.c", "line": 64 } }, { "caret": { "column": 10, "file": "bad-binary-ops.c", "line": 64 }, "finish": { "column": 21, "file": "bad-binary-ops.c", "line": 64 }, "label": "S {aka struct s}" }, { "caret": { "column": 25, "file": "bad-binary-ops.c", "line": 64 }, "finish": { "column": 36, "file": "bad-binary-ops.c", "line": 64 }, "label": "T {aka struct t}" } ], "message": "invalid operands to binary + ..." }
If a diagnostic contains fix-it hints, it has a fixits
array,
consisting of half-open intervals, similar to the output of
-fdiagnostics-parseable-fixits. For example, this diagnostic
with a replacement fix-it hint:
demo.c:8:15: error: 'struct s' has no member named 'colour'; did you mean 'color'? 8 | return ptr->colour; | ^~~~~~ | color
might be printed in JSON form as:
{ "children": [], "fixits": [ { "next": { "column": 21, "file": "demo.c", "line": 8 }, "start": { "column": 15, "file": "demo.c", "line": 8 }, "string": "color" } ], "kind": "error", "locations": [ { "caret": { "column": 15, "file": "demo.c", "line": 8 }, "finish": { "column": 20, "file": "demo.c", "line": 8 } } ], "message": "\u2018struct s\u2019 has no member named ..." }
where the fix-it hint suggests replacing the text from start
up
to but not including next
with string
's value. Deletions
are expressed via an empty value for string
, insertions by
having start
equal next
.