SPRUIG8J January 2018 – March 2024
One of the primary functions of the compiler and linker is to report diagnostic messages for the source program. A diagnostic message indicates that something may be wrong with the program. When the compiler or linker detects a suspect condition, it displays a message in the following format:
"file.c", line n : diagnostic severity : diagnostic message
| "file.c" | The name of the file involved |
| line n : | The line number where the diagnostic applies |
| diagnostic severity | The diagnostic message severity (severity category descriptions follow) |
| diagnostic message | The text that describes the problem |
Diagnostic messages have a severity, as follows:
Diagnostic messages are written to standard error with a form like the following example:
"test.c", line 5: error: a break statement may only be used within a loop or switch
break;
^By default, the source code line is not printed. Use the --verbose_diagnostics compiler option to display the source line and the error position. The above example makes use of this option.
The message identifies the file and line involved in the diagnostic, and the source line itself (with the position indicated by the ^ character) follows the message. If several diagnostic messages apply to one source line, each diagnostic has the form shown; the text of the source line is displayed several times, with an appropriate position indicated each time.
Long messages are wrapped to additional lines, when necessary.
You can use the --display_error_number command-line option to request that the diagnostic's numeric identifier be included in the diagnostic message. When displayed, the diagnostic identifier also indicates whether the diagnostic can have its severity overridden on the command line. If the severity can be overridden, the diagnostic identifier includes the suffix -D (for discretionary); otherwise, no suffix is present. For example:
"Test_name.c", line 7: error #64-D: declaration does not declare anything
struct {};
^
"Test_name.c", line 9: error #77: this declaration has no storage class or type specifier
xxxxx;
^Because errors are determined to be discretionary based on the severity in a specific context, an error can be discretionary in some cases and not in others. All warnings, remarks, and advice diagnostics are discretionary.
For some messages, a list of entities (functions, local variables, source files, etc.) is useful; the entities are listed following the initial error message:
"test.c", line 4: error: more than one instance of overloaded function "f"
matches the argument list:
function "f(int)"
function "f(float)"
argument types are: (double)
f(1.5);
^In some cases, additional context information is provided. Specifically, the context information is useful when the front end issues a diagnostic while doing a template instantiation or while generating a constructor, destructor, or assignment operator function. For example:
"test.c", line 7: error: "A::A()" is inaccessible
B x;
^
detected during implicit generation of "B::B()" at line 7Without the context information, it is difficult to determine to what the error refers.