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What's the purpose of declaring function as pointers?

This is a discussion on What's the purpose of declaring function as pointers? within the C Programming forums, part of the General Programming Boards category; Hi Mentors, I am bit confused as why does one need to declared the functions as pointers. For example I ...

  1. #1
    Registered User ankiit's Avatar
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    What's the purpose of declaring function as pointers?

    Hi Mentors,

    I am bit confused as why does one need to declared the functions as pointers.

    For example I was going through fgets functions which has the following prototype defined in stdio.h

    char *fgets(char *str, int size, FILE* file);

    Please provide your valuable inputs.

    Thanks
    Ankit

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    That's not an example of a function pointer. What 'fgets' does is return a char pointer.

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    For starters, the arguments of fgets() aren't function pointers. Look at the signal() syscall for an example of function pointers and it'll also tell you why 'n where they are applicable.

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    Registered User ankiit's Avatar
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    Quote Originally Posted by nonoob View Post
    That's not an example of a function pointer. What 'fgets' does is return a char pointer.
    but what does char *fgets () mean ?

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    means fgets returns a string.
    You can do
    Code:
    char *pnt;
    ...
    pnt = fgetc(buffer, 100, stream); /* returns a string */
    printf("String is %s\n", pnt);
    I'm not sure why one would want to look at that string if the buffer variable is designed to contain it. But there are times when the returned pointer is NULL - some error occurred.
    Last edited by nonoob; 02-03-2012 at 01:57 PM.

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    Quote Originally Posted by nonoob View Post
    means fgets returns a string.
    No, it means that fgets() returns a pointer to char.

    A string is something different from a pointer. By convention, however, if fgets() returns non-NULL, the data at that address is a collection of contiguous char's, with the last one zero (which is how strings are represented in the C standard library).

    fgets() returns a NULL pointer if an error occurs or, if no characters have been read, the end of the stream has been reached.
    quzah likes this.
    Right 98% of the time, and don't care about the other 3%.

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    spurious conceit MK27's Avatar
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    Quote Originally Posted by ankiit View Post
    I am bit confused as why does one need to declared the functions as pointers.
    A function can't really be declared as a pointer, but you can declare a pointer to a function. That would be a "function pointer", but as a few people have said, this isn't one.

    All functions have a type; it may be any type, but it must be the same type as the value returned by the function. If the function does not return anything, its type should be void. Note that this is not the same as void*; a void function returns nothing, but a void* function returns a pointer to a void type.

    The type of fgets() is char*, because fgets returns a pointer to a char type.

    A char pointer may point to the beginning of a string. In practice, it almost always is.
    Last edited by MK27; 02-03-2012 at 02:44 PM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  8. #8
    kotin
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    Hi ,

    I know some information about that function pointer that we can use them more in callback functions.

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    Registered User manasij7479's Avatar
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    Quote Originally Posted by nkrao123@gmail. View Post
    Hi ,

    I know some information about that function pointer that we can use them more in callback functions.
    Where did you see function pointers here ?
    Manasij Mukherjee | gcc-4.8.2 @Arch Linux
    Slow and Steady wins the race... if and only if :
    1.None of the other participants are fast and steady.
    2.The fast and unsteady suddenly falls asleep while running !



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