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Function pointer with named arguments?

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16

1

I recently came across a strange syntax in C program.

struct connector_agent_api
 bool (*receive)(slot *s, uint8_t *data, uint8_t length);

Is "receive" a function pointer?

If it is a function pointer, why does it have named arguments? Should it be like the following one?

bool (*receive)(slot *, uint8_t *, uint8_t);

It certainly compiled and being used in a library. I searched on internet a lot and tried to justify this kind of syntax. I still don't know why this thing can be compiled... :(

c function pointers

share|improve this question

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

• 
  
  
  

  
  20
  

  
  
  
  
  
  

  
  
  These names are for self-documentation only, they have no meaning for the functionality.
  
  – Eugene Sh.
  Apr 26 at 16:20
  

  
  
  
  


• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Note this is very much like a function declaration in a header file, where parameter names are optional and have no effect on the resulting program.
  
  – jdehesa
  Apr 26 at 16:21
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @EugeneSh. Same as for any other function declaration that's not a definition.
  
  – Konrad Rudolph
  Apr 26 at 21:04
  

  
  
  
  

add a comment | 

16

1

I recently came across a strange syntax in C program.

struct connector_agent_api
 bool (*receive)(slot *s, uint8_t *data, uint8_t length);

Is "receive" a function pointer?

If it is a function pointer, why does it have named arguments? Should it be like the following one?

bool (*receive)(slot *, uint8_t *, uint8_t);

It certainly compiled and being used in a library. I searched on internet a lot and tried to justify this kind of syntax. I still don't know why this thing can be compiled... :(

c function pointers

share|improve this question

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

• 
  
  
  

  
  20
  

  
  
  
  
  
  

  
  
  These names are for self-documentation only, they have no meaning for the functionality.
  
  – Eugene Sh.
  Apr 26 at 16:20
  

  
  
  
  


• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Note this is very much like a function declaration in a header file, where parameter names are optional and have no effect on the resulting program.
  
  – jdehesa
  Apr 26 at 16:21
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @EugeneSh. Same as for any other function declaration that's not a definition.
  
  – Konrad Rudolph
  Apr 26 at 21:04
  

  
  
  
  

add a comment | 

I recently came across a strange syntax in C program.

struct connector_agent_api
 bool (*receive)(slot *s, uint8_t *data, uint8_t length);

Is "receive" a function pointer?

If it is a function pointer, why does it have named arguments? Should it be like the following one?

bool (*receive)(slot *, uint8_t *, uint8_t);

It certainly compiled and being used in a library. I searched on internet a lot and tried to justify this kind of syntax. I still don't know why this thing can be compiled... :(

c function pointers

share|improve this question

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

struct connector_agent_api
 bool (*receive)(slot *s, uint8_t *data, uint8_t length);

bool (*receive)(slot *, uint8_t *, uint8_t);

share|improve this question

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

share|improve this question

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

edited Apr 26 at 16:24

John Kugelman

250k54410462

edited Apr 26 at 16:24

John Kugelman

250k54410462

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

asked Apr 26 at 16:18

ZuckerReisZuckerReis

857

2 Answers
2

active

oldest

votes

18

The names of arguments in a function pointer are optional, just as the names of arguments in a function declaration are optional. This is because parameter names if given are not used, so both formats are allowed.

In section 6.7.6.3 of the C standard regarding Function Declarators, which includes both function prototypes and function pointers, paragraph 6 states:

A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function.

The only place where function parameters require a name is in the actual definition of a function.

For a function definition, Section 6.9.1p5 states:

If the declarator includes a parameter type list, the
declaration of each parameter shall include an identifier, except
for the special case of a parameter list consisting of a single
parameter of type void , in which case there shall not be an
identifier. No declaration list shall follow.

share|improve this answer

edited Apr 26 at 18:49

answered Apr 26 at 16:31

dbushdbush

106k15111150

add a comment | 

4

What makes you think it is a strange syntax? It is a valid declaration as per C standard. The fact that the parameters are named is irrelevant. The naming of such parameters is optional in this case. It can be really helpful if you or someone else is using an IDE because it could display the complete prototype upon using the function pointer to call the function and thus give a hint to the coder about the arguments to be supplied.

share|improve this answer

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It is also helpful because this sort of struct is used to sort of fake object-like syntax. If the type is actually one meant for the functions to be invoked externally it helps to name the parameters as part of the documentation for that external interface. You are more likely to see code with unnamed parameters to function pointers when the pointers are a callback (rather than call-in).
  
  – SoronelHaetir
  Apr 27 at 4:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SoronelHaetir Thanks! I like your point on the call-back and call-in.
  
  – ZuckerReis
  Apr 28 at 19:39
  
  

  
  
  
  

add a comment | 

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18

The names of arguments in a function pointer are optional, just as the names of arguments in a function declaration are optional. This is because parameter names if given are not used, so both formats are allowed.

In section 6.7.6.3 of the C standard regarding Function Declarators, which includes both function prototypes and function pointers, paragraph 6 states:

A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function.

The only place where function parameters require a name is in the actual definition of a function.

For a function definition, Section 6.9.1p5 states:

If the declarator includes a parameter type list, the
declaration of each parameter shall include an identifier, except
for the special case of a parameter list consisting of a single
parameter of type void , in which case there shall not be an
identifier. No declaration list shall follow.

share|improve this answer

edited Apr 26 at 18:49

answered Apr 26 at 16:31

dbushdbush

106k15111150

add a comment | 

18

The names of arguments in a function pointer are optional, just as the names of arguments in a function declaration are optional. This is because parameter names if given are not used, so both formats are allowed.

In section 6.7.6.3 of the C standard regarding Function Declarators, which includes both function prototypes and function pointers, paragraph 6 states:

A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function.

The only place where function parameters require a name is in the actual definition of a function.

For a function definition, Section 6.9.1p5 states:

If the declarator includes a parameter type list, the
declaration of each parameter shall include an identifier, except
for the special case of a parameter list consisting of a single
parameter of type void , in which case there shall not be an
identifier. No declaration list shall follow.

share|improve this answer

edited Apr 26 at 18:49

answered Apr 26 at 16:31

dbushdbush

106k15111150

add a comment | 

The names of arguments in a function pointer are optional, just as the names of arguments in a function declaration are optional. This is because parameter names if given are not used, so both formats are allowed.

In section 6.7.6.3 of the C standard regarding Function Declarators, which includes both function prototypes and function pointers, paragraph 6 states:

A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function.

The only place where function parameters require a name is in the actual definition of a function.

For a function definition, Section 6.9.1p5 states:

If the declarator includes a parameter type list, the
declaration of each parameter shall include an identifier, except
for the special case of a parameter list consisting of a single
parameter of type void , in which case there shall not be an
identifier. No declaration list shall follow.

share|improve this answer

edited Apr 26 at 18:49

answered Apr 26 at 16:31

dbushdbush

106k15111150

share|improve this answer

edited Apr 26 at 18:49

answered Apr 26 at 16:31

dbushdbush

106k15111150

answered Apr 26 at 16:31

dbushdbush

106k15111150

answered Apr 26 at 16:31

dbushdbush

106k15111150

4

What makes you think it is a strange syntax? It is a valid declaration as per C standard. The fact that the parameters are named is irrelevant. The naming of such parameters is optional in this case. It can be really helpful if you or someone else is using an IDE because it could display the complete prototype upon using the function pointer to call the function and thus give a hint to the coder about the arguments to be supplied.

share|improve this answer

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It is also helpful because this sort of struct is used to sort of fake object-like syntax. If the type is actually one meant for the functions to be invoked externally it helps to name the parameters as part of the documentation for that external interface. You are more likely to see code with unnamed parameters to function pointers when the pointers are a callback (rather than call-in).
  
  – SoronelHaetir
  Apr 27 at 4:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SoronelHaetir Thanks! I like your point on the call-back and call-in.
  
  – ZuckerReis
  Apr 28 at 19:39
  
  

  
  
  
  

add a comment | 

4

What makes you think it is a strange syntax? It is a valid declaration as per C standard. The fact that the parameters are named is irrelevant. The naming of such parameters is optional in this case. It can be really helpful if you or someone else is using an IDE because it could display the complete prototype upon using the function pointer to call the function and thus give a hint to the coder about the arguments to be supplied.

share|improve this answer

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It is also helpful because this sort of struct is used to sort of fake object-like syntax. If the type is actually one meant for the functions to be invoked externally it helps to name the parameters as part of the documentation for that external interface. You are more likely to see code with unnamed parameters to function pointers when the pointers are a callback (rather than call-in).
  
  – SoronelHaetir
  Apr 27 at 4:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SoronelHaetir Thanks! I like your point on the call-back and call-in.
  
  – ZuckerReis
  Apr 28 at 19:39
  
  

  
  
  
  

add a comment | 

What makes you think it is a strange syntax? It is a valid declaration as per C standard. The fact that the parameters are named is irrelevant. The naming of such parameters is optional in this case. It can be really helpful if you or someone else is using an IDE because it could display the complete prototype upon using the function pointer to call the function and thus give a hint to the coder about the arguments to be supplied.

share|improve this answer

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

share|improve this answer

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

answered Apr 26 at 17:10

machine_1machine_1

2,69221332

answered Apr 26 at 17:10

machine_1machine_1

2,69221332