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Diffstat (limited to 'www/compatibility.html')
| -rw-r--r-- | www/compatibility.html | 101 |
1 files changed, 50 insertions, 51 deletions
diff --git a/www/compatibility.html b/www/compatibility.html index 725c52f..8bfaff1 100644 --- a/www/compatibility.html +++ b/www/compatibility.html @@ -19,10 +19,10 @@ <h1>Language Compatibility</h1> <!-- ======================================================================= --> -<p>Clang strives to both conform to current language standards (C99, - C++98) and also to implement many widely-used extensions available +<p>Clang strives to both conform to current language standards (up to C11 + and C++11) and also to implement many widely-used extensions available in other compilers, so that most correct code will "just work" when - compiler with Clang. However, Clang is more strict than other + compiled with Clang. However, Clang is more strict than other popular compilers, and may reject incorrect code that other compilers allow. This page documents common compatibility and portability issues with Clang to help you understand and fix the @@ -188,10 +188,9 @@ use the API calls instead of calls like <tt>__builtin_ia32_paddw128</tt>.</p> different type. Clang produces an error on similar code, e.g.,</p> <pre> -lvalue.c:2:3: error: assignment to cast is illegal, lvalue casts are not - supported +<b>lvalue.c:2:3: <span class="error">error:</span> assignment to cast is illegal, lvalue casts are not supported</b> (int*)addr = val; - ^~~~~~~~~~ ~ +<span class="caret"> ^~~~~~~~~~ ~</span> </pre> <p>To fix this problem, move the cast to the right-hand side. In this @@ -232,12 +231,12 @@ the stack is fresh, i.e. still zeroed.) Therefore, Clang rejects this code with a hard error:</p> <pre> -t.c:3:5: error: goto into protected scope +<b>t.c:3:5: <span class="error">error:</span> goto into protected scope</b> goto error; - ^ -t.c:5:15: note: jump bypasses setup of __block variable +<span class="caret"> ^</span> +<b>t.c:5:15: <span class="note">note:</note></b> jump bypasses setup of __block variable __block int result; - ^ +<span class="caret"> ^</span> </pre> <p>The fix is to rewrite the code to not require jumping into a @@ -308,10 +307,9 @@ rejects the instruction with this error message: </p> <pre> -<inline asm>:3:1: error: ambiguous instructions require an explicit suffix (could be 'addb', 'addw', 'addl', or 'addq') +<b><inline asm>:3:1: <span class="error">error:</span> ambiguous instructions require an explicit suffix (could be 'addb', 'addw', 'addl', or 'addq')</b> add $4, (%rax) -^ -1 error generated. +<span class="caret">^</span> </pre> <p>To fix this compatibility issue, add an explicit suffix to the instruction: @@ -331,9 +329,9 @@ can, among other things, be cast to a different type. Clang treats type-cast of <code>super</code>:</p> <pre> -super.m:11:12: error: cannot cast 'super' (it isn't an expression) +<b>super.m:11:12: <span class="error">error:</span> cannot cast 'super' (it isn't an expression)</b> [(Super*)super add:4]; - ~~~~~~~~^ +<span class="caret"> ~~~~~~~~^</span> </pre> <p>To fix this problem, remove the type cast, e.g.</p> @@ -352,10 +350,9 @@ Objective-C class may change over time as instance variables are added ABI:</p> <pre> -sizeof.m:4:14: error: invalid application of 'sizeof' to interface 'NSArray' in - non-fragile ABI +<b>sizeof.m:4:14: <span class="error">error:</span> invalid application of 'sizeof' to interface 'NSArray' in non-fragile ABI</b> int size = sizeof(NSArray); - ^ ~~~~~~~~~ +<span class="caret"> ^ ~~~~~~~~~</span> </pre> <p>Code that relies on the size of an Objective-C class is likely to @@ -377,12 +374,12 @@ this problem, use the Objective-C runtime API function internal Objective-C structures as implementation detail and won't do implicit conversions: <pre> -t.mm:11:2: error: no matching function for call to 'f' +<b>t.mm:11:2: <span class="error">error:</span> no matching function for call to 'f'</b> f((struct objc_object *)p); - ^ -t.mm:5:6: note: candidate function not viable: no known conversion from 'struct objc_object *' to 'id' for 1st argument +<span class="caret"> ^</span> +<b>t.mm:5:6: <span class="note">note:</note></b> candidate function not viable: no known conversion from 'struct objc_object *' to 'id' for 1st argument void f(id x); - ^ +<span class="caret"> ^</span> </pre> <p>Code should use types <tt>id</tt>, <tt>SEL</tt>, and <tt>Class</tt> @@ -465,15 +462,16 @@ int main() { <p>Clang complains: -<pre> <b>my_file.cpp:2:10: <span class="error">error:</span> call to function 'Multiply' that is neither visible in the template definition nor found by argument-dependent lookup</b> - return Multiply(x, x); - <span class="caret"> ^</span> - <b>my_file.cpp:10:3: <span class="note">note:</span> in instantiation of function template specialization 'Squared<int>' requested here</b> - Squared(5); - <span class="caret"> ^</span> - <b>my_file.cpp:5:5: <span class="note">note:</span> 'Multiply' should be declared prior to the call site</b> - int Multiply(int x, int y) { - <span class="caret"> ^</span> +<pre> +<b>my_file.cpp:2:10: <span class="error">error:</span> call to function 'Multiply' that is neither visible in the template definition nor found by argument-dependent lookup</b> + return Multiply(x, x); +<span class="caret"> ^</span> +<b>my_file.cpp:10:3: <span class="note">note:</span></b> in instantiation of function template specialization 'Squared<int>' requested here + Squared(5); +<span class="caret"> ^</span> +<b>my_file.cpp:5:5: <span class="note">note:</span></b> 'Multiply' should be declared prior to the call site +int Multiply(int x, int y) { +<span class="caret"> ^</span> </pre> <p>The C++ standard says that unqualified names like <q>Multiply</q> @@ -526,15 +524,16 @@ void Use() { <p>Again, Clang complains:</p> -<pre> <b>my_file2.cpp:5:13: <span class="error">error:</span> call to function 'operator<<' that is neither visible in the template definition nor found by argument-dependent lookup</b> - std::cout << value << "\n"; - <span class="caret"> ^</span> - <b>my_file2.cpp:17:3: <span class="error">note:</span> in instantiation of function template specialization 'Dump<ns::Data>' requested here</b> - Dump(ns::Data()); - <span class="caret"> ^</span> - <b>my_file2.cpp:12:15: <span class="error">note:</span> 'operator<<' should be declared prior to the call site or in namespace 'ns'</b> - std::ostream& operator<<(std::ostream& out, ns::Data data) { - <span class="caret"> ^</span> +<pre> +<b>my_file2.cpp:5:13: <span class="error">error:</span> call to function 'operator<<' that is neither visible in the template definition nor found by argument-dependent lookup</b> + std::cout << value << "\n"; +<span class="caret"> ^</span> +<b>my_file2.cpp:17:3: <span class="note">note:</span></b> in instantiation of function template specialization 'Dump<ns::Data>' requested here + Dump(ns::Data()); +<span class="caret"> ^</span> +<b>my_file2.cpp:12:15: <span class="note">note:</span></b> 'operator<<' should be declared prior to the call site or in namespace 'ns' +std::ostream& operator<<(std::ostream& out, ns::Data data) { +<span class="caret"> ^</span> </pre> <p>Just like before, unqualified lookup didn't find any declarations @@ -587,18 +586,18 @@ Clang correctly rejects it with the following errors (when <tt>Derived</tt> is eventually instantiated): <pre> -my_file.cpp:8:5: error: use of undeclared identifier 'DoThis' +<b>my_file.cpp:8:5: <span class="error">error:</span> use of undeclared identifier 'DoThis'</b> DoThis(x); - ^ +<span class="caret"> ^</span> this-> -my_file.cpp:2:8: note: must qualify identifier to find this declaration in dependent base class +<b>my_file.cpp:2:8: <span class="note">note:</note></b> must qualify identifier to find this declaration in dependent base class void DoThis(T x) {} - ^ -my_file.cpp:9:5: error: use of undeclared identifier 'DoThat' +<span class="caret"> ^</span> +<b>my_file.cpp:9:5: <span class="error">error:</span> use of undeclared identifier 'DoThat'</b> DoThat(x); - ^ +<span class="caret"> ^</span> this-> -my_file.cpp:3:15: note: must qualify identifier to find this declaration in dependent base class +<b>my_file.cpp:3:15: <span class="note">note:</note></b> must qualify identifier to find this declaration in dependent base class static void DoThat(T x) {} </pre> @@ -820,13 +819,13 @@ void g(Base *p) { <p>Clang produces the following error:</p> <pre> -downcast.mm:6:3: error: no matching function for call to 'f' +<b>downcast.mm:6:3: <span class="error">error:</span> no matching function for call to 'f'</b> f(p); - ^ -downcast.mm:4:6: note: candidate function not viable: cannot convert from +<span class="caret"> ^</span> +<b>downcast.mm:4:6: <span class="note">note:</note></b> candidate function not viable: cannot convert from superclass 'Base *' to subclass 'Derived *' for 1st argument void f(Derived *p); - ^ +<span class="caret"> ^</span> </pre> <p>If the downcast is actually correct (e.g., because the code has |
