What is the rationale behind the differences between the compiler diagnostics issued when it sees std::vector and std::vector
Clash Royale CLAN TAG#URR8PPP
Consider these two programs and their attempted compilations.
#include <vector>
int main()
std::vector<struct Typo> a; // Errors centered around `Typo` being an incomplete type
gcc 6.3, for example, gives error messages centered around Typo being an incomplete type, including
/usr/include/c++/6/bits/stl_vector.h:161:9: error: invalid use of incomplete type ‘
struct main()::Typo’
#include <vector>
int main()
std::vector<Typo> b; // Errors centred around `Typo` not being defined
gcc 6.3, for example, gives errors centered around Typo not being defined, including
prog.cpp:4:14: error:
‘Typo’was not declared in this scope
Both vector instantiations are errors of course, but what is the rationale for the differing diagnostic messages as cited in the program comments?
c++ compiler-errors
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
|
show 11 more comments
Consider these two programs and their attempted compilations.
#include <vector>
int main()
std::vector<struct Typo> a; // Errors centered around `Typo` being an incomplete type
gcc 6.3, for example, gives error messages centered around Typo being an incomplete type, including
/usr/include/c++/6/bits/stl_vector.h:161:9: error: invalid use of incomplete type ‘
struct main()::Typo’
#include <vector>
int main()
std::vector<Typo> b; // Errors centred around `Typo` not being defined
gcc 6.3, for example, gives errors centered around Typo not being defined, including
prog.cpp:4:14: error:
‘Typo’was not declared in this scope
Both vector instantiations are errors of course, but what is the rationale for the differing diagnostic messages as cited in the program comments?
c++ compiler-errors
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
1
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
2
@SombreroChicken: Am I astd::numeric_limits<Typo>::max()?
– Bathsheba
Jan 31 at 12:54
1
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
1
@Bathsheba Ratherstd::numeric_limits<Typo>::infinity().
– Sombrero Chicken
Jan 31 at 12:55
2
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06
|
show 11 more comments
Consider these two programs and their attempted compilations.
#include <vector>
int main()
std::vector<struct Typo> a; // Errors centered around `Typo` being an incomplete type
gcc 6.3, for example, gives error messages centered around Typo being an incomplete type, including
/usr/include/c++/6/bits/stl_vector.h:161:9: error: invalid use of incomplete type ‘
struct main()::Typo’
#include <vector>
int main()
std::vector<Typo> b; // Errors centred around `Typo` not being defined
gcc 6.3, for example, gives errors centered around Typo not being defined, including
prog.cpp:4:14: error:
‘Typo’was not declared in this scope
Both vector instantiations are errors of course, but what is the rationale for the differing diagnostic messages as cited in the program comments?
c++ compiler-errors
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
Consider these two programs and their attempted compilations.
#include <vector>
int main()
std::vector<struct Typo> a; // Errors centered around `Typo` being an incomplete type
gcc 6.3, for example, gives error messages centered around Typo being an incomplete type, including
/usr/include/c++/6/bits/stl_vector.h:161:9: error: invalid use of incomplete type ‘
struct main()::Typo’
#include <vector>
int main()
std::vector<Typo> b; // Errors centred around `Typo` not being defined
gcc 6.3, for example, gives errors centered around Typo not being defined, including
prog.cpp:4:14: error:
‘Typo’was not declared in this scope
Both vector instantiations are errors of course, but what is the rationale for the differing diagnostic messages as cited in the program comments?
c++ compiler-errors
c++ compiler-errors
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
edited Jan 31 at 13:06
Bathsheba
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
asked Jan 31 at 12:47
BathshebaBathsheba
179k27254382
179k27254382
1
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
2
@SombreroChicken: Am I astd::numeric_limits<Typo>::max()?
– Bathsheba
Jan 31 at 12:54
1
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
1
@Bathsheba Ratherstd::numeric_limits<Typo>::infinity().
– Sombrero Chicken
Jan 31 at 12:55
2
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06
|
show 11 more comments
1
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
2
@SombreroChicken: Am I astd::numeric_limits<Typo>::max()?
– Bathsheba
Jan 31 at 12:54
1
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
1
@Bathsheba Ratherstd::numeric_limits<Typo>::infinity().
– Sombrero Chicken
Jan 31 at 12:55
2
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06
1
1
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
2
2
@SombreroChicken: Am I a
std::numeric_limits<Typo>::max()?– Bathsheba
Jan 31 at 12:54
@SombreroChicken: Am I a
std::numeric_limits<Typo>::max()?– Bathsheba
Jan 31 at 12:54
1
1
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
1
1
@Bathsheba Rather
std::numeric_limits<Typo>::infinity().– Sombrero Chicken
Jan 31 at 12:55
@Bathsheba Rather
std::numeric_limits<Typo>::infinity().– Sombrero Chicken
Jan 31 at 12:55
2
2
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06
|
show 11 more comments
1 Answer
1
active
oldest
votes
struct Typo is an elaborated type specifier. That affects how name lookup works.
[basic.lookup.elab]
2: If the elaborated-type-specifier has no nested-name-specifier,
and unless the elaborated-type-specifier appears in a declaration with
the following form:class-key attribute-specifier-seq identifier ;
the identifier is looked up according to [basic.lookup.unqual] but
ignoring any non-type names that have been declared. If the
elaborated-type-specifier is introduced by the enum keyword and this
lookup does not find a previously declared type-name, the
elaborated-type-specifier is ill-formed. If the
elaborated-type-specifier is introduced by the class-key and this
lookup does not find a previously declared type-name, or if the
elaborated-type-specifier appears in a declaration with the form:class-key attribute-specifier-seq identifier ;
the elaborated-type-specifier is a declaration that introduces the
class-name as described in [basic.scope.pdecl].
So in std::vector<struct Typo> a;, because struct Typo does not find a previously declared Typo, it serves as a forward declaration for the type. And as such, its the vector instantiation that may1 complain the type it got is incomplete because it will try to do stuff with it.
While in std::vector<Typo> b;, looking up Typo finds nothing. There is no previous declaration for it, so its at this point a diagnostic should be issued that this identifier is undeclared.
1 - Depends on what standard you are compiling to, and what members of the vector you are using. Support for incomplete types has been added.
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
|
show 10 more comments
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1 Answer
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1 Answer
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oldest
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oldest
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votes
struct Typo is an elaborated type specifier. That affects how name lookup works.
[basic.lookup.elab]
2: If the elaborated-type-specifier has no nested-name-specifier,
and unless the elaborated-type-specifier appears in a declaration with
the following form:class-key attribute-specifier-seq identifier ;
the identifier is looked up according to [basic.lookup.unqual] but
ignoring any non-type names that have been declared. If the
elaborated-type-specifier is introduced by the enum keyword and this
lookup does not find a previously declared type-name, the
elaborated-type-specifier is ill-formed. If the
elaborated-type-specifier is introduced by the class-key and this
lookup does not find a previously declared type-name, or if the
elaborated-type-specifier appears in a declaration with the form:class-key attribute-specifier-seq identifier ;
the elaborated-type-specifier is a declaration that introduces the
class-name as described in [basic.scope.pdecl].
So in std::vector<struct Typo> a;, because struct Typo does not find a previously declared Typo, it serves as a forward declaration for the type. And as such, its the vector instantiation that may1 complain the type it got is incomplete because it will try to do stuff with it.
While in std::vector<Typo> b;, looking up Typo finds nothing. There is no previous declaration for it, so its at this point a diagnostic should be issued that this identifier is undeclared.
1 - Depends on what standard you are compiling to, and what members of the vector you are using. Support for incomplete types has been added.
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
|
show 10 more comments
struct Typo is an elaborated type specifier. That affects how name lookup works.
[basic.lookup.elab]
2: If the elaborated-type-specifier has no nested-name-specifier,
and unless the elaborated-type-specifier appears in a declaration with
the following form:class-key attribute-specifier-seq identifier ;
the identifier is looked up according to [basic.lookup.unqual] but
ignoring any non-type names that have been declared. If the
elaborated-type-specifier is introduced by the enum keyword and this
lookup does not find a previously declared type-name, the
elaborated-type-specifier is ill-formed. If the
elaborated-type-specifier is introduced by the class-key and this
lookup does not find a previously declared type-name, or if the
elaborated-type-specifier appears in a declaration with the form:class-key attribute-specifier-seq identifier ;
the elaborated-type-specifier is a declaration that introduces the
class-name as described in [basic.scope.pdecl].
So in std::vector<struct Typo> a;, because struct Typo does not find a previously declared Typo, it serves as a forward declaration for the type. And as such, its the vector instantiation that may1 complain the type it got is incomplete because it will try to do stuff with it.
While in std::vector<Typo> b;, looking up Typo finds nothing. There is no previous declaration for it, so its at this point a diagnostic should be issued that this identifier is undeclared.
1 - Depends on what standard you are compiling to, and what members of the vector you are using. Support for incomplete types has been added.
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
|
show 10 more comments
struct Typo is an elaborated type specifier. That affects how name lookup works.
[basic.lookup.elab]
2: If the elaborated-type-specifier has no nested-name-specifier,
and unless the elaborated-type-specifier appears in a declaration with
the following form:class-key attribute-specifier-seq identifier ;
the identifier is looked up according to [basic.lookup.unqual] but
ignoring any non-type names that have been declared. If the
elaborated-type-specifier is introduced by the enum keyword and this
lookup does not find a previously declared type-name, the
elaborated-type-specifier is ill-formed. If the
elaborated-type-specifier is introduced by the class-key and this
lookup does not find a previously declared type-name, or if the
elaborated-type-specifier appears in a declaration with the form:class-key attribute-specifier-seq identifier ;
the elaborated-type-specifier is a declaration that introduces the
class-name as described in [basic.scope.pdecl].
So in std::vector<struct Typo> a;, because struct Typo does not find a previously declared Typo, it serves as a forward declaration for the type. And as such, its the vector instantiation that may1 complain the type it got is incomplete because it will try to do stuff with it.
While in std::vector<Typo> b;, looking up Typo finds nothing. There is no previous declaration for it, so its at this point a diagnostic should be issued that this identifier is undeclared.
1 - Depends on what standard you are compiling to, and what members of the vector you are using. Support for incomplete types has been added.
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
struct Typo is an elaborated type specifier. That affects how name lookup works.
[basic.lookup.elab]
2: If the elaborated-type-specifier has no nested-name-specifier,
and unless the elaborated-type-specifier appears in a declaration with
the following form:class-key attribute-specifier-seq identifier ;
the identifier is looked up according to [basic.lookup.unqual] but
ignoring any non-type names that have been declared. If the
elaborated-type-specifier is introduced by the enum keyword and this
lookup does not find a previously declared type-name, the
elaborated-type-specifier is ill-formed. If the
elaborated-type-specifier is introduced by the class-key and this
lookup does not find a previously declared type-name, or if the
elaborated-type-specifier appears in a declaration with the form:class-key attribute-specifier-seq identifier ;
the elaborated-type-specifier is a declaration that introduces the
class-name as described in [basic.scope.pdecl].
So in std::vector<struct Typo> a;, because struct Typo does not find a previously declared Typo, it serves as a forward declaration for the type. And as such, its the vector instantiation that may1 complain the type it got is incomplete because it will try to do stuff with it.
While in std::vector<Typo> b;, looking up Typo finds nothing. There is no previous declaration for it, so its at this point a diagnostic should be issued that this identifier is undeclared.
1 - Depends on what standard you are compiling to, and what members of the vector you are using. Support for incomplete types has been added.
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
edited Jan 31 at 13:07
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
answered Jan 31 at 12:52
StoryTellerStoryTeller
99.3k12201271
99.3k12201271
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
|
show 10 more comments
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
1
1
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
elaborate type specifier - that's posh.
– Bathsheba
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
@Bathsheba - I'm not gonna complain :)
– StoryTeller
Jan 31 at 12:53
1
1
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
@Pi - No, I did not say that. The declaration is known. But the vector tries to use an incomplete type in a way that is not allowed (create objects of it, for instance).
– StoryTeller
Jan 31 at 12:57
1
1
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
@jrok DOHHH!!!!!!!!!!!!!!!!!!!! :) No more to add. Typo was well chosen. Thanks for pointing out :D
– P i
Jan 31 at 13:05
1
1
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
Ho man, that footnote killed me!
– YSC
Jan 31 at 16:51
|
show 10 more comments
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1
Because it's two different things? a) "You say there's a Typo, ok I get it, but it's incomplete". b) "There are no Typos around here, dude."
– jrok
Jan 31 at 12:52
2
@SombreroChicken: Am I a
std::numeric_limits<Typo>::max()?– Bathsheba
Jan 31 at 12:54
1
@user463035818 It doesn't matter, how is compiler supposed to know it's a typo?
– jrok
Jan 31 at 12:54
1
@Bathsheba Rather
std::numeric_limits<Typo>::infinity().– Sombrero Chicken
Jan 31 at 12:55
2
Edited to be two programs, since it seems that's what you're actually asking about, and to specify gcc 6.3.
– aschepler
Jan 31 at 13:06