amitavac@whileliesent-lm:~/data/prog/c++/template_ptr$g++ -v -o template template.cpp Using built-in specs. Target: i486-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu Thread model: posix gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) COLLECT_GCC_OPTIONS='-v' '-o' 'template' '-shared-libgcc' '-mtune=generic' '-march=i486' /usr/lib/gcc/i486-linux-gnu/4.4.3/cc1plus -quiet -v -D_GNU_SOURCE template.cpp -D_FORTIFY_SOURCE=2 -quiet -dumpbase template.cpp -mtune=generic -march=i486 -auxbase template -version -fstack-protector -o /tmp/ccZiqQ9b.s GNU C++ (Ubuntu 4.4.3-4ubuntu5) version 4.4.3 (i486-linux-gnu) compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1. GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 ignoring nonexistent directory "/usr/local/include/i486-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../i486-linux-gnu/include" ignoring nonexistent directory "/usr/include/i486-linux-gnu" #include "..." search starts here: #include <...> search starts here: /usr/include/c++/4.4 /usr/include/c++/4.4/i486-linux-gnu /usr/include/c++/4.4/backward /usr/local/include /usr/lib/gcc/i486-linux-gnu/4.4.3/include /usr/lib/gcc/i486-linux-gnu/4.4.3/include-fixed /usr/include End of search list. GNU C++ (Ubuntu 4.4.3-4ubuntu5) version 4.4.3 (i486-linux-gnu) compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1. GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 35224f2c24023afb0a5be7befe8d5f3f template.cpp: In member function ‘void MISC<T, P>::add(int)’: template.cpp:55: error: parse error in template argument list template.cpp:58: error: parse error in template argument list template.cpp:61: error: parse error in template argument list template.cpp:64: error: parse error in template argument list template.cpp: In member function ‘void MISC<T, P>::print(int)’: template.cpp:72: error: parse error in template argument list template.cpp:75: error: parse error in template argument list template.cpp:78: error: parse error in template argument list template.cpp:81: error: parse error in template argument list Following is the content of template.cpp (please let me know whats wrong with the following program): #include<stdint.h> #include<iostream> #include<vector> #include<set> using namespace std; template<typename T, typename P> class MISC{ private: vector<T> vec1; vector<T> vec2; set<T> st1; set<T> st2; vector<P> *ptr; private: template<vector<T>* vc> void addVecVals(){ for(T i=0; i<10;i++) { vc->push_back(i); } } template<set<T>* st> void addStVals(){ for(T i=0; i<10;i++) { st->insert(i); } } template<vector<T>* vc> void printVecVals(){ for(typename vector<T>::iterator i=vc->begin(), j=vc->end(); i!=j;++i) { cout<<"val = "<<*i<<" , "; } } template<set<T>* st> void printStVals(){ for(typename set<T>::iterator i=st->begin(), j=st->end(); i!=j;++i) { cout<<"val = "<<*i<<" , "; } } public: void add(int vecNum) { switch(vecNum) { case 0: //vecs. addVecVals<&vec1>(); break; case 1: addVecVals<&vec2>(); break; case 2: //sets addStVals<&st1>(); break; case 3: addStVals<&st2>(); break; default: break; } } void print(int vecNum) { switch(vecNum) { case 0: //vecs. printVecVals<&vec1>(); break; case 1: printVecVals<&vec2>(); break; case 2: //sets printStVals<&st1>(); break; case 3: printStVals<&st2>(); break; default: break; } } }; int main(void) { MISC<uint64_t, double> m; m.add(0); m.add(1); m.add(2); m.add(3); return 0; }
Created attachment 21176 [details] Code which is failing.
Created attachment 21177 [details] .s file generated by -save-temps
Created attachment 21178 [details] .ii file generated by -save-temps
The error message is not clear. The issue is that you are not using a constant expression for a template arugment. Template arguments are either constant expressions or types.
(In reply to comment #4) > The error message is not clear. The issue is that you are not using a constant > expression for a template arugment. Template arguments are either constant > expressions or types. > Whenever I will be using this kind of template in a class, the variable name is predefined. Now when I create an object and call the function, it will get the address offset and thus should be able to create an instance of that function with same prototype but different body, else for such cases we have to create different functions for each member. Can it be a new feature in g++ compiler? This will make function and objects as first class citizen in C++. We can create function at runtime with different object embedded in it. (I know it can be done by #define, but this is a better way I think.)
Honestly, nothing similar will happen any time soon, it means changing completely the semantics of templates. Maybe we can produce a better diagnostics, let's add Manuel in CC to hear his opinion...
Closing as invalid.
(In reply to comment #6) > Honestly, nothing similar will happen any time soon, it means changing > completely the semantics of templates. Maybe we can produce a better > diagnostics, let's add Manuel in CC to hear his opinion... The code is invalid but the diagnostic could be much better (I only have GCC 4.5.2, so perhaps it is better in trunk). Smaller testcase: template<typename T> class MISC{ public: T vec1; template<T* vc> void addVecVals(){}; void add(void) { addVecVals<&vec1>(); }; }; void foo(void) { MISC<int> m; m.add(); } Clang++ gives a somewhat better message: /tmp/webcompile/_14512_0.cc:6:22: error: no matching member function for call to 'addVecVals' void add(void) { addVecVals<&vec1>(); }; ^~~~~~~~~~~~~~~~~ /tmp/webcompile/_14512_0.cc:11:7: note: in instantiation of member function 'MISC<int>::add' requested here m.add(); ^ /tmp/webcompile/_14512_0.cc:5:26: note: candidate template ignored: invalid explicitly-specified argument for template parameter 'vc' template<T* vc> void addVecVals(){}; ^ 1 error generated. I would argue for reopening it...
Hey, you woke up! ;) Sure, let's re-open is a diagnostic issue, your call.
The problem seems to be the tentative parsing in cp_parse_template_id, which tries every crazy thing it can, and when nothing works, it just gives this catch all diagnostic. But debugging the C++ parser is an absolute pain, I hope someone with more patience takes a shot at this. The current diagnostic is just awful.
For the testcase in comment #8: Ok, this is interesting as at first I thought this was fixed in GCC 11 but then I looked to see what the different standards do as GCC 11's default is C++17. With C++17 and C++20, we get: <source>:8:34: error: use of 'this' in a constant expression 8 | void add(void) { addVecVals<&vec1>(); } | ^~~~ <source>: In instantiation of 'void MISC<T>::add() [with T = int]': <source>:13:10: required from here <source>:8:39: error: no matching function for call to 'MISC<int>::addVecVals<(&((MISC<int>*)this)->MISC<int>::vec1)>()' 8 | void add(void) { addVecVals<&vec1>(); } | ~~~~~~~~~~~~~~~~~^~ <source>:7:26: note: candidate: 'template<int* vc> void MISC<T>::addVecVals() [with T* vc = vc; T = int]' 7 | template<T* vc> void addVecVals(){} | ^~~~~~~~~~ <source>:7:26: note: template argument deduction/substitution failed: <source>:8:34: error: '&((MISC<int>*)this)->MISC<int>::vec1' is not a valid template argument of type 'int*' because '((MISC<int>*)this)->MISC<int>::vec1' is not a variable 8 | void add(void) { addVecVals<&vec1>(); } | ^~~~ But for C++98, C++11, C++14, we get: <source>: In member function 'void MISC<T>::add()': <source>:8:22: error: parse error in template argument list 8 | void add(void) { addVecVals<&vec1>(); } | ^~~~~~~~~~~~~~~~~