https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93716
Bug ID: 93716
Summary: [feature request] Improve error message for Classes
without a default constructor
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: volker.weissmann at gmx dot de
Target Milestone: ---
Consider the following C++ source code:
-------------------------------------
class NoDefaultConstr
{
public:
NoDefaultConstr(int i)
{
(void) i;
}
};
class BadClass
{
public:
NoDefaultConstr obj;
int othervar;
BadClass(int i):
othervar(17)
{
(void) i;
}
};
int main()
{
BadClass abc(123);
}
-------------------------------------
Compilation of the code above should fail. Compiling with g++ main.cpp fails
with the following output:
-------------------------------------
main.cpp: In constructor ‘BadClass::BadClass(int)’:
main.cpp:15:20: error: no matching function for call to
‘NoDefaultConstr::NoDefaultConstr()’
15 | othervar(17)
| ^
main.cpp:4:5: note: candidate: ‘NoDefaultConstr::NoDefaultConstr(int)’
4 | NoDefaultConstr(int i)
| ^~~~~~~~~~~~~~~
main.cpp:4:5: note: candidate expects 1 argument, 0 provided
main.cpp:1:7: note: candidate: ‘constexpr
NoDefaultConstr::NoDefaultConstr(const NoDefaultConstr&)’
1 | class NoDefaultConstr
| ^~~~~~~~~~~~~~~
main.cpp:1:7: note: candidate expects 1 argument, 0 provided
main.cpp:1:7: note: candidate: ‘constexpr
NoDefaultConstr::NoDefaultConstr(NoDefaultConstr&&)’
main.cpp:1:7: note: candidate expects 1 argument, 0 provided
-------------------------------------
Compiling fails as it should, but it would be nice if the error message would
be a bit more helpful. e.g.:
-------------------------------------
main.cpp: In constructor ‘BadClass::BadClass(int)’:
main.cpp:15:20: error: no matching function for call to
‘NoDefaultConstr::NoDefaultConstr()’
15 | othervar(17)
| ^
main.cpp:12:23: note: Because of declaration of object ‘obj’
12 | NoDefaultConstr obj;
|
main.cpp:4:5: note: candidate: ‘NoDefaultConstr::NoDefaultConstr(int)’
4 | NoDefaultConstr(int i)
| ^~~~~~~~~~~~~~~
main.cpp:4:5: note: candidate expects 1 argument, 0 provided
main.cpp:1:7: note: candidate: ‘constexpr
NoDefaultConstr::NoDefaultConstr(const NoDefaultConstr&)’
1 | class NoDefaultConstr
| ^~~~~~~~~~~~~~~
main.cpp:1:7: note: candidate expects 1 argument, 0 provided
main.cpp:1:7: note: candidate: ‘constexpr
NoDefaultConstr::NoDefaultConstr(NoDefaultConstr&&)’
main.cpp:1:7: note: candidate expects 1 argument, 0 provided
-------------------------------------
The reason why I do not like gcc's error message is that it never mentions the
line 12 or the variable obj. Clang in comparison mentions both and has imho a
much nicer error message:
---------------------
main.cpp:14:5: error: constructor for 'BadClass' must explicitly initialize the
member 'obj' which does not have a default constructor
BadClass(int i):
^
main.cpp:12:21: note: member is declared here
NoDefaultConstr obj;
^
main.cpp:1:7: note: 'NoDefaultConstr' declared here
class NoDefaultConstr
^
---------------------
