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gcc flag warning as error Wakeman, Ohio

Some users try to use -pedantic to check programs for strict ISO C conformance. c gcc compiler-warnings share|improve this question edited Sep 24 '14 at 15:51 Pro Backup 375420 asked Jul 19 '12 at 12:51 Saurabh Verma 2,32042245 1 I strongly suggest trying to Do you really care about compatibility with 30 year old compilers? In traditional C macro replacement takes place within string literals, but does not in ISO C.

Not the answer you're looking for? C++). This warning is enabled by default. -Wshift-negative-valueWarn if left shifting a negative value. For example, the call to sprintf below is diagnosed because even with both a and b equal to zero, the terminating NUL character ('\0') appended by the function to the destination

Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. GCC will guess that format attributes might be appropriate for any function that calls a function like vprintf or vscanf, but this might not always be the case, and some functions In order to get a warning about an unused function parameter, you must either specify `-Wextra -Wunused' (note that `-Wall' implies `-Wunused'), or separately specify -Wunused-parameter. -WuninitializedWarn if an automatic variable This is a common cause of error, as programmers often forget that this type is signed on some machines.

This includes standard functions, and others specified by format attributes (see Function Attributes), in the printf, scanf, strftime and strfmon (an X/Open extension, not in the C standard) families (or other As a result, you may get a warning even when there is in fact no problem because longjmp cannot in fact be called at the place which would cause a problem. But obviously, if I already knew about all the warnings and which ones are useful (and which ones aren't), then there would've been nothing to ask. Use of these macros in user code might normally lead to spurious warnings, however GCC's integrated preprocessor has enough context to avoid warning in these cases.

char buf [64]; new (buf) int[64]; This warning is enabled by default. -Wplacement-new=1This is the default warning level of -Wplacement-new. GNU C assigns these types a size of 1, for convenience in calculations with void * pointers and pointers to functions. -Wbad-function-cast (C only)Warn whenever a function call is cast to In existing C++ implementations, however, offsetof typically gives meaningful results even when applied to certain kinds of non-POD types. (Such as a simple struct that fails to be a POD type Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives.

more hot questions question feed lang-c about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture / Recreation The ISO type of an integer constant has a different width or signedness from its traditional type. Level 2: Aggressive, quick, not too precise. As a GNU extension, the latter case is accepted without a warning unless -Wpedantic is used.

more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed 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. -Wfloat-equalWarn if floating point values are Source: http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Warning-Options.html share|improve this answer answered Jul 19 '12 at 12:55 orlp 53.4k20120207 add a comment| up vote 1 down vote accepted Thanks for all the helpful suggestions. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the

This option also warns when a non-volatile automatic variable might be changed by a call to longjmp. This warning is enabled by -Wall. -WformatCheck calls to printf and scanf, etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the To suppress the warning, you need to provide a default case with assert(0) or similar code. However, -Wno-error=foo does not imply anything. -Wfatal-errorsThis option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages.

To get other -Wextra warnings without this one, use `-Wextra -Wno-missing-field-initializers'. -Wmissing-noreturnWarn about functions which might be candidates for attribute noreturn. ISO C prohibits qualified void return types on function definitions, so such return types always receive a warning even without this option. It cannot know where longjmp will be called; in fact, a signal handler could call it at any point in the code. Also warn about any return statement with no return-value in a function whose return-type is not void.

Traditional C lacks a separate namespace for labels. Unlike level 1, it only warns when an address is taken. And I still have no idea if this list is comprehensive. It is implied by -Wall and by -pedantic, which can be disabled with -Wno-pointer-sign. -Wstack-protectorThis option is only active when -fstack-protector is active.

That should work unless the -Werror is passed after the flags you set in CFLAGS in the makefile. –Daniel Fischer Jul 19 '12 at 12:59 Can this be enabled Many warnings are issued only if you ask for them, with one of the -W options (for instance, -Wall requests a variety of useful warnings). However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. void f (int a, int b) { char buf [12]; sprintf (buf, "a = %i, b = %i\n", a, b); } -Wformat-length=2Level 2 warns also about calls that might overflow the

Also warn about constructions where there may be confusion to which if statement an else branch belongs. Also, they do not occur for structures, unions or arrays, even when they are in registers. With this option, they are rejected. -pedantic does not cause warning messages for use of the alternate keywords whose names begin and end with __. the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a format attribute to avoid

Related 71How to suppress GCC warnings from library headers?41Is using #pragma warning push/pop the right way to temporarily alter warning level?2Suppress GCC warning “extra tokens at end of #include directive”3warning: data The formats are checked against the format features supported by GNU libc version 2.2. GCC code review policies do not allow new options without documentation, so the docs should be comprehensive. –Jonathan Wakely Sep 22 '15 at 12:14 add a comment| up vote 1 down For instance, in this code, the variable f.x in struct bar will be misaligned even though struct bar does not itself have the packed attribute: struct foo { int x; char

ISO 10646 defines the NFKC normalization scheme to convert all these into a standard form as well, and GCC will warn if your code is not in NFKC if you use The C standard specifies that zero-length formats are allowed. -Wformat-nonliteralIf -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the Hot Network Questions How much interest should I pay on a loan from a friend? Disabling them will let you move on in the short perspective, but you'll never know if these issues will come back to haunt you in the long run. –Benjamin Bannier Jul

Using this command line option tells GCC to emit warnings from system headers as if they occurred in user code. Generate a 6 character string from a 15 character alphabet Word for someone who keeps a group in good shape? How to handle a senior developer diva who seems unaware that his skills are obsolete? Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that “Between the previous and next sequence point an object shall have its stored value modified

Most are for C++ though. I found the shadowing one helpful, so it's not like they're useless just because they're turned off). –Mehrdad Jul 30 '12 at 3:35 add a comment| up vote 3 down vote