Why isn't it a compile-time error to return a nullptr as a std::string?Access Violation when sending a 0 int literal to a const string parameterAvoiding improper std::string initialization with NULL const char* using g++Why does constructing std::string(0) not emit a compiler warning?How to concatenate a std::string and an int?What's the best way to trim std::string?How to convert std::string to lower case?How to convert a std::string to const char* or char*?std::wstring VS std::stringconvert a char* to std::stringWhy is “using namespace std;” considered bad practice?Why does outputting a class with a conversion operator not work for std::string?STL map<string, string>, assign 0 value to a key causes compile errorVector push_back error when compiling
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Why isn't it a compile-time error to return a nullptr as a std::string?
Access Violation when sending a 0 int literal to a const string parameterAvoiding improper std::string initialization with NULL const char* using g++Why does constructing std::string(0) not emit a compiler warning?How to concatenate a std::string and an int?What's the best way to trim std::string?How to convert std::string to lower case?How to convert a std::string to const char* or char*?std::wstring VS std::stringconvert a char* to std::stringWhy is “using namespace std;” considered bad practice?Why does outputting a class with a conversion operator not work for std::string?STL map<string, string>, assign 0 value to a key causes compile errorVector push_back error when compiling
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Due to a bug, I just found out that this code compiles fine on with Visual Studio 17 and probably on other compilers as well. Now I'm curious why?
#include <iostream>
#include <string>
std::string foo()
return nullptr;
int main()
auto s = foo();
std::cout << s << std::endl;
I could imagine it is because the std::basic_string c'tor could be invoked with a char* and while returning an implicit conversion from ptr to std::string occurs (with NULL as argument and then goes poof). Am I on the right way?
c++ stdstring
edited 1 hour ago
Cody Gray♦
198k37391481
asked 13 hours ago
TaronTaron
502520
add a comment |
Due to a bug, I just found out that this code compiles fine on with Visual Studio 17 and probably on other compilers as well. Now I'm curious why?
#include <iostream>
#include <string>
std::string foo()
return nullptr;
int main()
auto s = foo();
std::cout << s << std::endl;
I could imagine it is because the std::basic_string c'tor could be invoked with a char* and while returning an implicit conversion from ptr to std::string occurs (with NULL as argument and then goes poof). Am I on the right way?
c++ stdstring
edited 1 hour ago
Cody Gray♦
198k37391481
asked 13 hours ago
TaronTaron
502520
1
it is probably indeed passingnullptras the parameter for a pointer
– Tarick Welling
13 hours ago
2
It compiles, but you get a runtime error.
– t.niese
13 hours ago
7
It would probably be beneficial to add astring (nullptr_t) = deletector, just so this error is caught at compile time. I don't think legitimate programs would break due to that.
– MSalters
12 hours ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago
add a comment |
Due to a bug, I just found out that this code compiles fine on with Visual Studio 17 and probably on other compilers as well. Now I'm curious why?
#include <iostream>
#include <string>
std::string foo()
return nullptr;
int main()
auto s = foo();
std::cout << s << std::endl;
I could imagine it is because the std::basic_string c'tor could be invoked with a char* and while returning an implicit conversion from ptr to std::string occurs (with NULL as argument and then goes poof). Am I on the right way?
c++ stdstring
edited 1 hour ago
Cody Gray♦
198k37391481
asked 13 hours ago
TaronTaron
502520
Due to a bug, I just found out that this code compiles fine on with Visual Studio 17 and probably on other compilers as well. Now I'm curious why?
#include <iostream>
#include <string>
std::string foo()
return nullptr;
int main()
auto s = foo();
std::cout << s << std::endl;
I could imagine it is because the std::basic_string c'tor could be invoked with a char* and while returning an implicit conversion from ptr to std::string occurs (with NULL as argument and then goes poof). Am I on the right way?
c++ stdstring
c++ stdstring
edited 1 hour ago
Cody Gray♦
198k37391481
asked 13 hours ago
TaronTaron
502520
edited 1 hour ago
Cody Gray♦
198k37391481
asked 13 hours ago
TaronTaron
502520
edited 1 hour ago
Cody Gray♦
198k37391481
edited 1 hour ago
Cody Gray♦
198k37391481
edited 1 hour ago
Cody Gray♦
198k37391481
198k37391481
asked 13 hours ago
TaronTaron
502520
asked 13 hours ago
TaronTaron
502520
asked 13 hours ago
TaronTaron
502520
502520
1
it is probably indeed passingnullptras the parameter for a pointer
– Tarick Welling
13 hours ago
2
It compiles, but you get a runtime error.
– t.niese
13 hours ago
7
It would probably be beneficial to add astring (nullptr_t) = deletector, just so this error is caught at compile time. I don't think legitimate programs would break due to that.
– MSalters
12 hours ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago
add a comment |
1
it is probably indeed passingnullptras the parameter for a pointer
– Tarick Welling
13 hours ago
2
It compiles, but you get a runtime error.
– t.niese
13 hours ago
7
It would probably be beneficial to add astring (nullptr_t) = deletector, just so this error is caught at compile time. I don't think legitimate programs would break due to that.
– MSalters
12 hours ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago
1
1
it is probably indeed passing
nullptr as the parameter for a pointer– Tarick Welling
13 hours ago
it is probably indeed passing
nullptr as the parameter for a pointer– Tarick Welling
13 hours ago
2
2
It compiles, but you get a runtime error.
– t.niese
13 hours ago
It compiles, but you get a runtime error.
– t.niese
13 hours ago
7
7
It would probably be beneficial to add a
string (nullptr_t) = delete ctor, just so this error is caught at compile time. I don't think legitimate programs would break due to that.– MSalters
12 hours ago
It would probably be beneficial to add a
string (nullptr_t) = delete ctor, just so this error is caught at compile time. I don't think legitimate programs would break due to that.– MSalters
12 hours ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago
add a comment |
2 Answers
2
active
oldest
votes
Yes, your assumption is right, checking std::basic_string constructors #5 will be called:
basic_string( const CharT* s,
const Allocator& alloc = Allocator() );
Note that passing nullptr invokes undefined behavior as stated in the standard and the notes :
The behavior is
undefined if[s, s + Traits::length(s))is not a valid range (for
example, ifsis a null pointer).
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
add a comment |
Why shouldn't it compile? std::string has the following constructor:
string(const CharT* s, const Allocator& alloc = Allocator());
that constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s. The constructor is not explicit, so the implicit conversion from nullptr to std::string is indeed possible.
answered 13 hours ago
EvgEvg
5,56831841
1
Please note that passing null is UB
– Richard Critten
12 hours ago
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only fornullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.
– Evg
12 hours ago
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Yes, your assumption is right, checking std::basic_string constructors #5 will be called:
basic_string( const CharT* s,
const Allocator& alloc = Allocator() );
Note that passing nullptr invokes undefined behavior as stated in the standard and the notes :
The behavior is
undefined if[s, s + Traits::length(s))is not a valid range (for
example, ifsis a null pointer).
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
add a comment |
Yes, your assumption is right, checking std::basic_string constructors #5 will be called:
basic_string( const CharT* s,
const Allocator& alloc = Allocator() );
Note that passing nullptr invokes undefined behavior as stated in the standard and the notes :
The behavior is
undefined if[s, s + Traits::length(s))is not a valid range (for
example, ifsis a null pointer).
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
add a comment |
Yes, your assumption is right, checking std::basic_string constructors #5 will be called:
basic_string( const CharT* s,
const Allocator& alloc = Allocator() );
Note that passing nullptr invokes undefined behavior as stated in the standard and the notes :
The behavior is
undefined if[s, s + Traits::length(s))is not a valid range (for
example, ifsis a null pointer).
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
Yes, your assumption is right, checking std::basic_string constructors #5 will be called:
basic_string( const CharT* s,
const Allocator& alloc = Allocator() );
Note that passing nullptr invokes undefined behavior as stated in the standard and the notes :
The behavior is
undefined if[s, s + Traits::length(s))is not a valid range (for
example, ifsis a null pointer).
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
edited 13 hours ago
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
answered 13 hours ago
Sombrero ChickenSombrero Chicken
26.3k33484
26.3k33484
add a comment |
add a comment |
Why shouldn't it compile? std::string has the following constructor:
string(const CharT* s, const Allocator& alloc = Allocator());
that constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s. The constructor is not explicit, so the implicit conversion from nullptr to std::string is indeed possible.
answered 13 hours ago
EvgEvg
5,56831841
1
Please note that passing null is UB
– Richard Critten
12 hours ago
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only fornullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.
– Evg
12 hours ago
add a comment |
Why shouldn't it compile? std::string has the following constructor:
string(const CharT* s, const Allocator& alloc = Allocator());
that constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s. The constructor is not explicit, so the implicit conversion from nullptr to std::string is indeed possible.
answered 13 hours ago
EvgEvg
5,56831841
1
Please note that passing null is UB
– Richard Critten
12 hours ago
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only fornullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.
– Evg
12 hours ago
add a comment |
Why shouldn't it compile? std::string has the following constructor:
string(const CharT* s, const Allocator& alloc = Allocator());
that constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s. The constructor is not explicit, so the implicit conversion from nullptr to std::string is indeed possible.
answered 13 hours ago
EvgEvg
5,56831841
Why shouldn't it compile? std::string has the following constructor:
string(const CharT* s, const Allocator& alloc = Allocator());
that constructs the string with the contents initialized with a copy of the null-terminated character string pointed to by s. The constructor is not explicit, so the implicit conversion from nullptr to std::string is indeed possible.
answered 13 hours ago
EvgEvg
5,56831841
edited 12 hours ago
answered 13 hours ago
EvgEvg
5,56831841
answered 13 hours ago
EvgEvg
5,56831841
answered 13 hours ago
EvgEvg
5,56831841
5,56831841
1
Please note that passing null is UB
– Richard Critten
12 hours ago
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only fornullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.
– Evg
12 hours ago
add a comment |
1
Please note that passing null is UB
– Richard Critten
12 hours ago
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only fornullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.
– Evg
12 hours ago
1
1
Please note that passing null is UB
– Richard Critten
12 hours ago
Please note that passing null is UB
– Richard Critten
12 hours ago
7
7
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only for
nullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.– Evg
12 hours ago
@RichardCritten, it definitely is. But the question was why this code compiles, not what happens if the code is executed. UB will happen not only for
nullptr, but for any pointer that doesn't point to the beginning of a null-terminated string.– Evg
12 hours ago
add a comment |
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1
it is probably indeed passing
nullptras the parameter for a pointer– Tarick Welling
13 hours ago
2
It compiles, but you get a runtime error.
– t.niese
13 hours ago
7
It would probably be beneficial to add a
string (nullptr_t) = deletector, just so this error is caught at compile time. I don't think legitimate programs would break due to that.– MSalters
12 hours ago
Related, Why does constructing std::string(0) not emit a compiler warning?, Access Violation when sending a 0 int literal to a const string parameter, Avoiding improper std::string initialization with NULL const char* using g++, How to best protect from 0 passed to std::string parameters?, etc.
– jww
17 mins ago