Can we declare structure object at file scope before the structure definition?
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According to the code given below and the answer for it:
Question: Which of the following structure declarations will throw an error?
struct temp { char c; } s;
int main(void) {}
struct temp { char c; };
struct temp s;
int main(void) {}
struct temp s;
struct temp { char c; };
int main(void) {}
None of the above.
Answer: 4
Is this correct? Can we declare a structure object first and only then the structure definition?
c
edited Apr 21 at 7:30
StoryTeller
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
|
show 4 more comments
According to the code given below and the answer for it:
Question: Which of the following structure declarations will throw an error?
struct temp { char c; } s;
int main(void) {}
struct temp { char c; };
struct temp s;
int main(void) {}
struct temp s;
struct temp { char c; };
int main(void) {}
None of the above.
Answer: 4
Is this correct? Can we declare a structure object first and only then the structure definition?
c
edited Apr 21 at 7:30
StoryTeller
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
1
You’re not supposed to be able to compile an empty structure body. In (c) there is no typestruct tempwhensis nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.
– Jonathan Leffler
Apr 21 at 7:07
2
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I addedint mainand a structure member, and it still compiles with no warnings. I also added a body tomainthat accesses the structure member, no complaints. I'm as surprised as the OP.
– Barmar
Apr 21 at 7:10
1
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
2
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15
|
show 4 more comments
According to the code given below and the answer for it:
Question: Which of the following structure declarations will throw an error?
struct temp { char c; } s;
int main(void) {}
struct temp { char c; };
struct temp s;
int main(void) {}
struct temp s;
struct temp { char c; };
int main(void) {}
None of the above.
Answer: 4
Is this correct? Can we declare a structure object first and only then the structure definition?
c
edited Apr 21 at 7:30
StoryTeller
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
According to the code given below and the answer for it:
Question: Which of the following structure declarations will throw an error?
struct temp { char c; } s;
int main(void) {}
struct temp { char c; };
struct temp s;
int main(void) {}
struct temp s;
struct temp { char c; };
int main(void) {}
None of the above.
Answer: 4
Is this correct? Can we declare a structure object first and only then the structure definition?
c
c
edited Apr 21 at 7:30
StoryTeller
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Apr 21 at 7:30
StoryTeller
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Apr 21 at 7:30
StoryTeller
107k14224288
edited Apr 21 at 7:30
StoryTeller
107k14224288
edited Apr 21 at 7:30
StoryTeller
107k14224288
107k14224288
asked Apr 21 at 6:49
DSWDSW
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked Apr 21 at 6:49
DSWDSW
564
asked Apr 21 at 6:49
DSWDSW
564
564
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
DSW is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
1
You’re not supposed to be able to compile an empty structure body. In (c) there is no typestruct tempwhensis nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.
– Jonathan Leffler
Apr 21 at 7:07
2
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I addedint mainand a structure member, and it still compiles with no warnings. I also added a body tomainthat accesses the structure member, no complaints. I'm as surprised as the OP.
– Barmar
Apr 21 at 7:10
1
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
2
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15
|
show 4 more comments
3
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
1
You’re not supposed to be able to compile an empty structure body. In (c) there is no typestruct tempwhensis nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.
– Jonathan Leffler
Apr 21 at 7:07
2
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I addedint mainand a structure member, and it still compiles with no warnings. I also added a body tomainthat accesses the structure member, no complaints. I'm as surprised as the OP.
– Barmar
Apr 21 at 7:10
1
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
2
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15
3
3
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
1
1
You’re not supposed to be able to compile an empty structure body. In (c) there is no type
struct temp when s is nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.– Jonathan Leffler
Apr 21 at 7:07
You’re not supposed to be able to compile an empty structure body. In (c) there is no type
struct temp when s is nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.– Jonathan Leffler
Apr 21 at 7:07
2
2
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I added
int main and a structure member, and it still compiles with no warnings. I also added a body to main that accesses the structure member, no complaints. I'm as surprised as the OP.– Barmar
Apr 21 at 7:10
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I added
int main and a structure member, and it still compiles with no warnings. I also added a body to main that accesses the structure member, no complaints. I'm as surprised as the OP.– Barmar
Apr 21 at 7:10
1
1
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
2
2
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15
|
show 4 more comments
1 Answer
1
active
oldest
votes
Yeah, C is weird sometimes. Because that variable is at file scope and has no initializer or storage class specifier, it constitutes a tentative defintion. The C standard defines it as follows:
6.9.2 External object definitions
A declaration of an identifier for an object that has file scope
without an initializer, and without a storage-class specifier or with
the storage-class specifier static, constitutes a tentative
definition. If a translation unit contains one or more tentative
definitions for an identifier, and the translation unit contains no
external definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation
unit, with an initializer equal to 0.
I emphasized the relevant part. Because there is no initializer on your variable, it's as though you'd written it at the very end of the file and initialized to zero. The physical layout of the file is immaterial, because logically, the definition of the structure type is available at the end of the file.
So the answer is indeed (4). I wouldn't write code like that in real life however, this is terribly confusing in the C eco-system where near everything must be pre-declared to be used.
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
add a comment |
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Yeah, C is weird sometimes. Because that variable is at file scope and has no initializer or storage class specifier, it constitutes a tentative defintion. The C standard defines it as follows:
6.9.2 External object definitions
A declaration of an identifier for an object that has file scope
without an initializer, and without a storage-class specifier or with
the storage-class specifier static, constitutes a tentative
definition. If a translation unit contains one or more tentative
definitions for an identifier, and the translation unit contains no
external definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation
unit, with an initializer equal to 0.
I emphasized the relevant part. Because there is no initializer on your variable, it's as though you'd written it at the very end of the file and initialized to zero. The physical layout of the file is immaterial, because logically, the definition of the structure type is available at the end of the file.
So the answer is indeed (4). I wouldn't write code like that in real life however, this is terribly confusing in the C eco-system where near everything must be pre-declared to be used.
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
add a comment |
Yeah, C is weird sometimes. Because that variable is at file scope and has no initializer or storage class specifier, it constitutes a tentative defintion. The C standard defines it as follows:
6.9.2 External object definitions
A declaration of an identifier for an object that has file scope
without an initializer, and without a storage-class specifier or with
the storage-class specifier static, constitutes a tentative
definition. If a translation unit contains one or more tentative
definitions for an identifier, and the translation unit contains no
external definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation
unit, with an initializer equal to 0.
I emphasized the relevant part. Because there is no initializer on your variable, it's as though you'd written it at the very end of the file and initialized to zero. The physical layout of the file is immaterial, because logically, the definition of the structure type is available at the end of the file.
So the answer is indeed (4). I wouldn't write code like that in real life however, this is terribly confusing in the C eco-system where near everything must be pre-declared to be used.
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
add a comment |
Yeah, C is weird sometimes. Because that variable is at file scope and has no initializer or storage class specifier, it constitutes a tentative defintion. The C standard defines it as follows:
6.9.2 External object definitions
A declaration of an identifier for an object that has file scope
without an initializer, and without a storage-class specifier or with
the storage-class specifier static, constitutes a tentative
definition. If a translation unit contains one or more tentative
definitions for an identifier, and the translation unit contains no
external definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation
unit, with an initializer equal to 0.
I emphasized the relevant part. Because there is no initializer on your variable, it's as though you'd written it at the very end of the file and initialized to zero. The physical layout of the file is immaterial, because logically, the definition of the structure type is available at the end of the file.
So the answer is indeed (4). I wouldn't write code like that in real life however, this is terribly confusing in the C eco-system where near everything must be pre-declared to be used.
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
Yeah, C is weird sometimes. Because that variable is at file scope and has no initializer or storage class specifier, it constitutes a tentative defintion. The C standard defines it as follows:
6.9.2 External object definitions
A declaration of an identifier for an object that has file scope
without an initializer, and without a storage-class specifier or with
the storage-class specifier static, constitutes a tentative
definition. If a translation unit contains one or more tentative
definitions for an identifier, and the translation unit contains no
external definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration of that
identifier, with the composite type as of the end of the translation
unit, with an initializer equal to 0.
I emphasized the relevant part. Because there is no initializer on your variable, it's as though you'd written it at the very end of the file and initialized to zero. The physical layout of the file is immaterial, because logically, the definition of the structure type is available at the end of the file.
So the answer is indeed (4). I wouldn't write code like that in real life however, this is terribly confusing in the C eco-system where near everything must be pre-declared to be used.
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
edited Apr 21 at 7:33
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
answered Apr 21 at 7:16
StoryTellerStoryTeller
107k14224288
107k14224288
add a comment |
add a comment |
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3
All the functions shown are non-standard for the whole of the current millennium. All the structures are malformed. None of the code should compile.
– Jonathan Leffler
Apr 21 at 7:00
1
You’re not supposed to be able to compile an empty structure body. In (c) there is no type
struct tempwhensis nominally defined, so the variable shouldn’t be definable. There might be a get-out-of-jail-free card somewhere; I don’t have a C compiler on my iPhone.– Jonathan Leffler
Apr 21 at 7:07
2
@JonathanLeffler The question is about the order of declarations, the structure members are irrelevant. I added
int mainand a structure member, and it still compiles with no warnings. I also added a body tomainthat accesses the structure member, no complaints. I'm as surprised as the OP.– Barmar
Apr 21 at 7:10
1
I’m asleep. My robot is responding now. If there’s still a controversy in the morning, I’ll look. If you ever needed evidence of why multichoice questions are abominable, this illustrates the point. You can’t present reasoning in an exam.
– Jonathan Leffler
Apr 21 at 7:13
2
@jonathan: Empty structures are a GCC extension to C.
– rici
Apr 21 at 7:15