| 287 | | For a particular file, |
| 288 | | |
| 289 | | #pragma GCC system_ // No warnings from all this file, considered a system header. |
| 290 | | |
| 291 | | or option --isystem |
| 292 | | |
| 293 | | The -isystem command line option adds its argument to the list of directories to search for headers, just like -I. Any headers found in that directory will be considered system headers. |
| | 287 | === Suppressing Warnings === |
| | 288 | ==== Supressing Warnings For A File By Making GCC See It As A System Header ==== |
| | 289 | For a particular file, you can turn off all warnings including most warnings generated by the expansion of macros specified in a file by putting the following in a file |
| | 290 | |
| | 291 | #pragma GCC system_header // File considered a system header. |
| | 292 | |
| | 293 | Note that this works differently depending on the version of GCC prior to version 4.6 it needed to be put near the beginning of the file and before any code. All code in the file after the pragma is seen will be considered system code. Since 4.6, it can be specified anywhere in the file, and code that precedes the pragma in the file will be unaffected. The intent of declaring a file a system header, is for operating system specific code that can't be strictly conforming C or C++. This should not be seen as a handy way of turning off bothersome warnings. Many ('''most?''') warnings point to real issues and should be dealt with appropriately. |
| | 294 | |
| | 295 | You can also turn off warnings for all files in a directory, by putting the directory into the include search path with -i instead of -I |
| | 296 | |
| | 297 | The -idirectoryName command line option adds its argument to the list of directories to search for headers, just like -I. Any headers found in that directory will be considered system headers. It also has the side effect of changing the inclusion order, in that all files included from directories specified with -i are included '''after''' files included from directories specified via -I. If the directory is specified with both -I and -i it is still only searched after normal includes as part of the system include directories. This may be appropriate if you have to deal with other's spotty code that generates a lot of warnings that you can't fix. |
| | 298 | |
| | 299 | If you turn off warnings for files that are shared with your users, you need to be able to see the warnings yourself so that as new problems arise you will see them. You can turn on warnings back on for system headers with: |
| 297 | | is effective until the end of the file. |
| 298 | | |
| 299 | | Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option will not warn about unknown pragmas in system headers—for that, -Wunknown-pragmas must also be used. |
| 300 | | |
| 301 | | The GCC docs say: "Also, while it is syntactically valid to put these pragmas anywhere in your sources, the only supported location for them is before any data or functions are defined. Doing otherwise may result in unpredictable results depending on how the optimizer manages your sources." |
| 302 | | |
| 303 | | This might only mean you can't use them inside functions or class definitions, but it seems to imply that using them after a function definition leads to undefined behavior. Thus, even if we knew what setting to turn the warning back to (perhaps the warning wasn't enabled in the first place!), we might not be able to turn them back on. |
| 304 | | |
| 305 | | <toolset>gcc:<cxxflags>-fdiagnostics-show-option # find out which options controls this warning (GCC >= 4.3) |
| 306 | | |
| 307 | | #if defined(__GNUC__) // GCC 4.3 and higher. |
| 308 | | #pragma GCC diagnostic ignored "-Wdeprecated-declarations" |
| 309 | | #endif |
| 310 | | |
| 311 | | But that doesn't quite work, how do you know that the user wants -Wdeprecated-declarations to be set to "warning" after the include? |
| 312 | | Could be the user has disabled that one on the command line, in which case if we turn it back on, that's as annoying for the end user as warnings from Boost! There was a time when some MSVC std lib headers behaved like that, and believe me it was *seriously* annoying :-( |
| | 303 | Print warning messages for constructs found in system header files that would normally not be seen. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option will not warn about unknown pragmas in system headers—for that, -Wunknown-pragmas must also be used. |
| | 304 | |
| | 305 | ==== Turning off warnings locally ==== |
| | 306 | So. Suppose you are getting a warning and have checked the code and are '''sure''' that it's a spurious warning. There's nothing wrong. '''If''' the warning is controllable via a command line -W option, then you can (if you have GCC version '''4.2''' or newer) turn it off temporarily. First you need to find out what the option might be, then if it exists turn it off via a pragma. How you do this varies a bit with GCC version. |
| | 307 | |
| | 308 | -fdiagnostics-show-option:: |
| | 309 | In GCC, for versions 4.3 and higher, this option instructs the diagnostic machinery to add text to each diagnostic emitted, which indicates which command line option directly controls that diagnostic, when such an option is known to the diagnostic machinery. |
| | 310 | #pragma GCC diagnostic push:: |
| | 311 | Available since GCC version 4.6, this pragma lets you remember diagnostic options in place at a particular time. This pragma can occur on any line of a file. |
| | 312 | #pragma GCC diagnostic pop:: |
| | 313 | Available since GCC version 4.6, this pragma lets you restore diagnostic options that were remembered by a diagnostic push. This pragma can occur on any line of a file. |
| | 314 | #pragma GCC diagnostic [warning|error|ignored] OPTION:: |
| | 315 | After GCC version 4.1 and before GCC version 4.6 this could be specified at file scope outside of any functions, classes, unions, structs, or methods, to change the behavior when a particular class of error was seen. For GCC version 4.6 and later, it can be put in any line of a file, and affects from that position forward. For any supported version, it only works with warnings that have explicit -W arguments, use -fdiagnostic-show-option to find out which one to use. An example: #pragma GCC diagnostic ignored "-Wdeprecated-declarations" |
| | 316 | |
| | 317 | So prior to 4.6 just put near the top of the file something like: |
| | 318 | |
| | 319 | #pragma GCC diagnostic ignored "-Wdeprecated-declarations |
| | 320 | |
| | 321 | For version 4.6 or later, you can insert this around the line that causes the spurious warning: |
| | 322 | |
| | 323 | #pragma GCC diagnostic push |
| | 324 | #pragma GCC diagnostic ignored "-Wdeprecated-declarations" |
| | 325 | |
| | 326 | // Next you would have your code that generates the spurious warning |
| | 327 | |
| | 328 | #pragma GCC diagnostic pop |
| | 329 | |
| | 330 | === Turning on Warnings === |
