Warn about the following: char s[3] = "foo"; Initializing a char array with a string literal of the same length as the size of the array is usually a mistake. Rarely is the case where one wants to create a non-terminated character sequence from a string literal. In some cases, for writing faster code, one may want to use arrays instead of pointers, since that removes the need for storing an array of pointers apart from the strings themselves. char *log_levels[] = { "info", "warning", "err" }; vs. char log_levels[][7] = { "info", "warning", "err" }; This forces the programmer to specify a size, which might change if a new entry is later added. Having no way to enforce null termination is very dangerous, however, so it is useful to have a warning for this, so that the compiler can make sure that the programmer didn't make any mistakes. This warning catches the bug above, so that the programmer will be able to fix it and write: char log_levels[][8] = { "info", "warning", "err" }; This warning already existed as part of -Wc++-compat, but this patch allows enabling it separately. It is also included in -Wextra, since it may not always be desired (when unterminated character sequences are wanted), but it's likely to be desired in most cases. Since Wc++-compat now includes this warning, the test has to be modified to expect the text of the new warning too, in . gcc/c-family/ChangeLog: * c.opt: Add -Wunterminated-string-initialization. gcc/c/ChangeLog: * c-typeck.cc (digest_init): Separate warnings about character arrays being initialized as unterminated character sequences with string literals, from -Wc++-compat, into a new warning, -Wunterminated-string-initialization. gcc/ChangeLog: * doc/invoke.texi: Document the new -Wunterminated-string-initialization. gcc/testsuite/ChangeLog: * gcc.dg/Wcxx-compat-14.c: Adapt the test to match the new text of the warning, which doesn't say anything about C++ anymore. * gcc.dg/Wunterminated-string-initialization.c: New test. Link: Link: Link: Acked-by: Doug McIlroy [Sandra: The documentation parts of the patch are OK.] Reviewed-by: Sandra Loosemore Cc: "G. Branden Robinson" Cc: Ralph Corderoy Cc: Dave Kemper Cc: Larry McVoy Cc: Andrew Pinski Cc: Jonathan Wakely Cc: Andrew Clayton Cc: Martin Uecker Cc: David Malcolm Cc: Mike Stump Cc: Joseph Myers Signed-off-by: Alejandro Colomar --- Hi! I've added a changelog to the commit message, as requested by Sandra, and noted her review. Have a lovely day! Alex Range-diff against v7: 1: c0f3ffcca7a ! 1: 06236d0aa05 C, ObjC: Add -Wunterminated-string-initialization @@ Commit message Since Wc++-compat now includes this warning, the test has to be modified to expect the text of the new warning too, in . + gcc/c-family/ChangeLog: + + * c.opt: Add -Wunterminated-string-initialization. + + gcc/c/ChangeLog: + + * c-typeck.cc (digest_init): Separate warnings about character + arrays being initialized as unterminated character sequences + with string literals, from -Wc++-compat, into a new warning, + -Wunterminated-string-initialization. + + gcc/ChangeLog: + + * doc/invoke.texi: Document the new + -Wunterminated-string-initialization. + + gcc/testsuite/ChangeLog: + + * gcc.dg/Wcxx-compat-14.c: Adapt the test to match the new text + of the warning, which doesn't say anything about C++ anymore. + * gcc.dg/Wunterminated-string-initialization.c: New test. + Link: Link: Link: Acked-by: Doug McIlroy + [Sandra: The documentation parts of the patch are OK.] + Reviewed-by: Sandra Loosemore Cc: "G. Branden Robinson" Cc: Ralph Corderoy Cc: Dave Kemper @@ Commit message Cc: David Malcolm Cc: Mike Stump Cc: Joseph Myers - Cc: Sandra Loosemore Signed-off-by: Alejandro Colomar ## gcc/c-family/c.opt ## gcc/c-family/c.opt | 4 ++++ gcc/c/c-typeck.cc | 6 +++--- gcc/doc/invoke.texi | 20 ++++++++++++++++++- gcc/testsuite/gcc.dg/Wcxx-compat-14.c | 2 +- .../Wunterminated-string-initialization.c | 6 ++++++ 5 files changed, 33 insertions(+), 5 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt index 44b9c862c14..3837021747b 100644 --- a/gcc/c-family/c.opt +++ b/gcc/c-family/c.opt @@ -1407,6 +1407,10 @@ Wunsuffixed-float-constants C ObjC Var(warn_unsuffixed_float_constants) Warning Warn about unsuffixed float constants. +Wunterminated-string-initialization +C ObjC Var(warn_unterminated_string_initialization) Warning LangEnabledBy(C ObjC,Wextra || Wc++-compat) +Warn about character arrays initialized as unterminated character sequences with a string literal. + Wunused C ObjC C++ ObjC++ LangEnabledBy(C ObjC C++ ObjC++,Wall) ; documented in common.opt diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc index e55e887da14..7df9de819ed 100644 --- a/gcc/c/c-typeck.cc +++ b/gcc/c/c-typeck.cc @@ -8399,11 +8399,11 @@ digest_init (location_t init_loc, tree type, tree init, tree origtype, pedwarn_init (init_loc, 0, ("initializer-string for array of %qT " "is too long"), typ1); - else if (warn_cxx_compat + else if (warn_unterminated_string_initialization && compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0) - warning_at (init_loc, OPT_Wc___compat, + warning_at (init_loc, OPT_Wunterminated_string_initialization, ("initializer-string for array of %qT " - "is too long for C++"), typ1); + "is too long"), typ1); if (compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0) { unsigned HOST_WIDE_INT size diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 146b40414b0..4e85311851f 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -410,7 +410,9 @@ Objective-C and Objective-C++ Dialects}. -Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs -Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas --Wunsuffixed-float-constants -Wunused +-Wunsuffixed-float-constants +-Wunterminated-string-initialization +-Wunused -Wunused-but-set-parameter -Wunused-but-set-variable -Wunused-const-variable -Wunused-const-variable=@var{n} -Wunused-function -Wunused-label -Wunused-local-typedefs @@ -6264,6 +6266,7 @@ name is still supported, but the newer name is more descriptive.) -Wredundant-move @r{(only for C++)} -Wtype-limits -Wuninitialized +-Wunterminated-string-initialization -Wshift-negative-value @r{(in C++11 to C++17 and in C99 and newer)} -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)}} @@ -8281,6 +8284,21 @@ arithmetic that may yield out of bounds values. This warning level may give a larger number of false positives and is deactivated by default. @end table +@opindex Wunterminated-string-initialization +@opindex Wno-unterminated-string-initialization +@item -Wunterminated-string-initialization @r{(C and Objective-C only)} +Warn about character arrays +initialized as unterminated character sequences +with a string literal. +For example: + +@smallexample +char arr[3] = "foo"; +@end smallexample + +This warning is enabled by @option{-Wextra} and @option{-Wc++-compat}. +In C++, such initializations are an error. + @opindex Warray-compare @opindex Wno-array-compare @item -Warray-compare diff --git a/gcc/testsuite/gcc.dg/Wcxx-compat-14.c b/gcc/testsuite/gcc.dg/Wcxx-compat-14.c index 23783711be6..6df0ee197cc 100644 --- a/gcc/testsuite/gcc.dg/Wcxx-compat-14.c +++ b/gcc/testsuite/gcc.dg/Wcxx-compat-14.c @@ -2,5 +2,5 @@ /* { dg-options "-Wc++-compat" } */ char a1[] = "a"; -char a2[1] = "a"; /* { dg-warning "C\[+\]\[+\]" } */ +char a2[1] = "a"; /* { dg-warning "initializer-string for array of 'char' is too long" } */ char a3[2] = "a"; diff --git a/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c b/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c new file mode 100644 index 00000000000..13d5dbc6640 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c @@ -0,0 +1,6 @@ +/* { dg-do compile } */ +/* { dg-options "-Wunterminated-string-initialization" } */ + +char a1[] = "a"; +char a2[1] = "a"; /* { dg-warning "initializer-string for array of 'char' is too long" } */ +char a3[2] = "a"; -- 2.43.0