Warning: ISO C++ forbids converting a string constant to ‘char*’ for a static `constexpr char*` data...
This question already has an answer here:
constexpr const vs constexpr variables? [duplicate]
3 answers
Why does this code return a warning
warning: ISO C++ forbids converting a string constant to ‘char*’
[-Wwrite-strings]
if
A constexpr specifier used in an object declaration or non-static
member function (until C++14) implies const. A constexpr specifier used in a function or static member variable (since C++17) declaration implies inline.
(cppreference.com)
#include <cassert>
#include <string>
#include <iostream>
struct A
{
// warning: ISO C++ forbids converting a string constant to ‘char*’
static constexpr char* name_ = "A";
static constexpr char* name() { return name_; };
};
int main()
{};
If I add a const after constexpr, the warning is gone:
#include <cassert>
#include <string>
#include <iostream>
struct A
{
static constexpr const char* name_ = "A";
static constexpr const char* name() { return name_; };
};
int main()
{};
With g++ --version = g++ (GCC) 8.2.1 20181127,
compilation g++ -O3 -std=c++2a -Wall main.cpp -o main.
Does the constexpr not imply const on static data members?
c++ c++11 static constexpr
asked Jan 18 at 16:47
tmarictmaric
2,7382052
marked as duplicate by Community♦ Jan 19 at 11:54
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
add a comment |
This question already has an answer here:
constexpr const vs constexpr variables? [duplicate]
3 answers
Why does this code return a warning
warning: ISO C++ forbids converting a string constant to ‘char*’
[-Wwrite-strings]
if
A constexpr specifier used in an object declaration or non-static
member function (until C++14) implies const. A constexpr specifier used in a function or static member variable (since C++17) declaration implies inline.
(cppreference.com)
#include <cassert>
#include <string>
#include <iostream>
struct A
{
// warning: ISO C++ forbids converting a string constant to ‘char*’
static constexpr char* name_ = "A";
static constexpr char* name() { return name_; };
};
int main()
{};
If I add a const after constexpr, the warning is gone:
#include <cassert>
#include <string>
#include <iostream>
struct A
{
static constexpr const char* name_ = "A";
static constexpr const char* name() { return name_; };
};
int main()
{};
With g++ --version = g++ (GCC) 8.2.1 20181127,
compilation g++ -O3 -std=c++2a -Wall main.cpp -o main.
Does the constexpr not imply const on static data members?
c++ c++11 static constexpr
asked Jan 18 at 16:47
tmarictmaric
2,7382052
marked as duplicate by Community♦ Jan 19 at 11:54
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50
add a comment |
This question already has an answer here:
constexpr const vs constexpr variables? [duplicate]
3 answers
Why does this code return a warning
warning: ISO C++ forbids converting a string constant to ‘char*’
[-Wwrite-strings]
if
A constexpr specifier used in an object declaration or non-static
member function (until C++14) implies const. A constexpr specifier used in a function or static member variable (since C++17) declaration implies inline.
(cppreference.com)
#include <cassert>
#include <string>
#include <iostream>
struct A
{
// warning: ISO C++ forbids converting a string constant to ‘char*’
static constexpr char* name_ = "A";
static constexpr char* name() { return name_; };
};
int main()
{};
If I add a const after constexpr, the warning is gone:
#include <cassert>
#include <string>
#include <iostream>
struct A
{
static constexpr const char* name_ = "A";
static constexpr const char* name() { return name_; };
};
int main()
{};
With g++ --version = g++ (GCC) 8.2.1 20181127,
compilation g++ -O3 -std=c++2a -Wall main.cpp -o main.
Does the constexpr not imply const on static data members?
c++ c++11 static constexpr
asked Jan 18 at 16:47
tmarictmaric
2,7382052
This question already has an answer here:
constexpr const vs constexpr variables? [duplicate]
3 answers
Why does this code return a warning
warning: ISO C++ forbids converting a string constant to ‘char*’
[-Wwrite-strings]
if
A constexpr specifier used in an object declaration or non-static
member function (until C++14) implies const. A constexpr specifier used in a function or static member variable (since C++17) declaration implies inline.
(cppreference.com)
#include <cassert>
#include <string>
#include <iostream>
struct A
{
// warning: ISO C++ forbids converting a string constant to ‘char*’
static constexpr char* name_ = "A";
static constexpr char* name() { return name_; };
};
int main()
{};
If I add a const after constexpr, the warning is gone:
#include <cassert>
#include <string>
#include <iostream>
struct A
{
static constexpr const char* name_ = "A";
static constexpr const char* name() { return name_; };
};
int main()
{};
With g++ --version = g++ (GCC) 8.2.1 20181127,
compilation g++ -O3 -std=c++2a -Wall main.cpp -o main.
Does the constexpr not imply const on static data members?
This question already has an answer here:
constexpr const vs constexpr variables? [duplicate]
3 answers
c++ c++11 static constexpr
c++ c++11 static constexpr
asked Jan 18 at 16:47
tmarictmaric
2,7382052
asked Jan 18 at 16:47
tmarictmaric
2,7382052
edited Jan 18 at 17:15
tmaric
asked Jan 18 at 16:47
tmarictmaric
2,7382052
asked Jan 18 at 16:47
tmarictmaric
2,7382052
asked Jan 18 at 16:47
tmarictmaric
2,7382052
2,7382052
marked as duplicate by Community♦ Jan 19 at 11:54
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by Community♦ Jan 19 at 11:54
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50
add a comment |
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50
add a comment |
2 Answers
2
active
oldest
votes
constexpr does imply const, but in this case it applies const to the "wrong thing".
constexpr char*
is basically the same as
char * const
which is a constant pointer to a non-const char. This won't work because string literals have the type const char[N] so it would cast away the constness of the array elements.
constexpr const char*
on the other hand, is basically the same as
char const * const
which is a constant pointer to a constant char, which is what you want as it preserves the constness of the elements.
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
add a comment |
There is a usual difference between a constant pointer and a pointer to constant. By making your constexpr char* you made a pointer itself a constexpr (and, of course, const), but it still attempts to point at non-const character - and this is wrong, as string literals are const. Solution:
constexpr const char* ch = "StackOverflow!";
Which declares a constexpr pointer to const.
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
1
I remember the ruleconstbinds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses.constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.
– Eljay
Jan 18 at 17:03
add a comment |
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
constexpr does imply const, but in this case it applies const to the "wrong thing".
constexpr char*
is basically the same as
char * const
which is a constant pointer to a non-const char. This won't work because string literals have the type const char[N] so it would cast away the constness of the array elements.
constexpr const char*
on the other hand, is basically the same as
char const * const
which is a constant pointer to a constant char, which is what you want as it preserves the constness of the elements.
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
add a comment |
constexpr does imply const, but in this case it applies const to the "wrong thing".
constexpr char*
is basically the same as
char * const
which is a constant pointer to a non-const char. This won't work because string literals have the type const char[N] so it would cast away the constness of the array elements.
constexpr const char*
on the other hand, is basically the same as
char const * const
which is a constant pointer to a constant char, which is what you want as it preserves the constness of the elements.
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
add a comment |
constexpr does imply const, but in this case it applies const to the "wrong thing".
constexpr char*
is basically the same as
char * const
which is a constant pointer to a non-const char. This won't work because string literals have the type const char[N] so it would cast away the constness of the array elements.
constexpr const char*
on the other hand, is basically the same as
char const * const
which is a constant pointer to a constant char, which is what you want as it preserves the constness of the elements.
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
constexpr does imply const, but in this case it applies const to the "wrong thing".
constexpr char*
is basically the same as
char * const
which is a constant pointer to a non-const char. This won't work because string literals have the type const char[N] so it would cast away the constness of the array elements.
constexpr const char*
on the other hand, is basically the same as
char const * const
which is a constant pointer to a constant char, which is what you want as it preserves the constness of the elements.
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
edited Jan 18 at 17:46
Remy Lebeau
336k18259453
336k18259453
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
answered Jan 18 at 16:52
NathanOliverNathanOliver
92.4k16129195
92.4k16129195
add a comment |
add a comment |
There is a usual difference between a constant pointer and a pointer to constant. By making your constexpr char* you made a pointer itself a constexpr (and, of course, const), but it still attempts to point at non-const character - and this is wrong, as string literals are const. Solution:
constexpr const char* ch = "StackOverflow!";
Which declares a constexpr pointer to const.
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
1
I remember the ruleconstbinds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses.constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.
– Eljay
Jan 18 at 17:03
add a comment |
There is a usual difference between a constant pointer and a pointer to constant. By making your constexpr char* you made a pointer itself a constexpr (and, of course, const), but it still attempts to point at non-const character - and this is wrong, as string literals are const. Solution:
constexpr const char* ch = "StackOverflow!";
Which declares a constexpr pointer to const.
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
1
I remember the ruleconstbinds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses.constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.
– Eljay
Jan 18 at 17:03
add a comment |
There is a usual difference between a constant pointer and a pointer to constant. By making your constexpr char* you made a pointer itself a constexpr (and, of course, const), but it still attempts to point at non-const character - and this is wrong, as string literals are const. Solution:
constexpr const char* ch = "StackOverflow!";
Which declares a constexpr pointer to const.
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
There is a usual difference between a constant pointer and a pointer to constant. By making your constexpr char* you made a pointer itself a constexpr (and, of course, const), but it still attempts to point at non-const character - and this is wrong, as string literals are const. Solution:
constexpr const char* ch = "StackOverflow!";
Which declares a constexpr pointer to const.
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
answered Jan 18 at 16:50
SergeyASergeyA
43k53886
43k53886
1
I remember the ruleconstbinds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses.constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.
– Eljay
Jan 18 at 17:03
add a comment |
1
I remember the ruleconstbinds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses.constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.
– Eljay
Jan 18 at 17:03
1
1
I remember the rule
const binds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses. constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.– Eljay
Jan 18 at 17:03
I remember the rule
const binds to the thing to its immediate left (unless its first, in which case it binds to the thing to its immediate right). In my code, I tend to favor the general case, rather than the except-to-the-general rule in the parentheses. constexpr, when I use it (not frequently), I always put on the left as the first thing. I've not been bitten by the OP's situation yet.– Eljay
Jan 18 at 17:03
add a comment |
stackoverflow.com/questions/28845058/…
– Mat
Jan 18 at 16:50
stackoverflow.com/questions/14116003/…
– Brandon Lyons
Jan 18 at 16:50