Function pointer with named arguments?





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16















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




















  • 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


















16















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




















  • 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














16












16








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
















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




c function pointers






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Apr 26 at 16:24









John Kugelman

253k55412464




253k55412464










asked Apr 26 at 16:18









ZuckerReisZuckerReis

857




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














  • 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








20




20





These names are for self-documentation only, they have no meaning for the functionality.

– Eugene Sh.
Apr 26 at 16:20





These names are for self-documentation only, they have no meaning for the functionality.

– Eugene Sh.
Apr 26 at 16:20




7




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





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




2





@EugeneSh. Same as for any other function declaration that's not a definition.

– Konrad Rudolph
Apr 26 at 21:04





@EugeneSh. Same as for any other function declaration that's not a definition.

– Konrad Rudolph
Apr 26 at 21:04












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

































    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



















    • 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














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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    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






























      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




























        18












        18








        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















        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














        share|improve this answer



        share|improve this answer








        edited Apr 26 at 18:49

























        answered Apr 26 at 16:31









        dbushdbush

        107k15113151




        107k15113151

























            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



















            • 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


















            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



















            • 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
















            4












            4








            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













            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












            share|improve this answer



            share|improve this answer










            answered Apr 26 at 17:10









            machine_1machine_1

            2,74621332




            2,74621332








            • 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
















            • 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










            1




            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





            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







            @SoronelHaetir Thanks! I like your point on the call-back and call-in.

            – ZuckerReis
            Apr 28 at 19:39




















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