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determining size of pointed to array

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jephthah

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determining size of pointed to array

May 14th, 2009

im going to risk getting a beating, because this is something i should (used to?) know...

anyhoo, given a function, how do you tell the size of the array that is passed? obviously trying to find the sizeof the pointer doesn't work (it returns the size of the pointer, duh)

but im having a brainfart trying to remember how to find the size of the passed array...

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
void myFunction (char * myString) 
{
    size_t len = sizeof(myString) 
    // gives size of pointer, not string
 
}
void myFunction (char * myString) 
{
    size_t len = sizeof(myString) 
    // gives size of pointer, not string

}

assume the string being pointed to is properly declared and of a significant length.

.

Last edited by jephthah; May 14th, 2009 at 3:32 pm.

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Narue

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Re: determining size of pointed to array

May 14th, 2009

>given a function, how do you tell the size of the array that is passed?
Given a function where the only parameter is a pointer to the first element of said array, you don't. There's no portable method, which is why the usual advice is a second parameter with the size:

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
void myfunction(char * pointerToString, size_t size)
void myfunction(char * pointerToString, size_t size)

I'm here to prove you wrong.

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jephthah

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Re: determining size of pointed to array

May 14th, 2009

er. i was hoping that wasnt the only answer.

oh, well, it's not a big deal. i just thoguht there was some clever trick that i had forgotten.

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winrawr

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Re: determining size of pointed to array

May 14th, 2009

okay wait, even though this thread is solved, if it's a string couldn't you use strlen? Or just int length = 0; while(length++,*myString++); ?

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Narue

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Re: determining size of pointed to array

May 14th, 2009

Good point. I was assuming jephthah wanted the capacity of an array, but that might have been an unwarranted assumption.

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jephthah

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Re: determining size of pointed to array

May 14th, 2009

no, i dont want a length of some arbitrary string, that may or may not be null-terminated

Narue was right: i wanted the size of the entire array.

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winrawr

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Re: determining size of pointed to array

May 14th, 2009

alright, just throwing it out there

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jephthah

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Re: determining size of pointed to array

May 14th, 2009

s'cool. thanks

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lolguy

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Re: determining size of pointed to array

May 15th, 2009

you can do also

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
void get_size(char *buffer,int size)
{
       fgets(buffer,size,stdin);
}
int main(void)
{
       char buffer[100];
       get_size(buffer,sizeof buffer);
}
void get_size(char *buffer,int size)
{
       fgets(buffer,size,stdin);
}
int main(void)
{
       char buffer[100];
       get_size(buffer,sizeof buffer);
}

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Aia

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Re: determining size of pointed to array

#10

May 15th, 2009

lolguy> you can do also
Did you read post number two before?
Did you notice that the thread is marked as solved? Which unless you are sure something has been overlooked, you should learn to leave alone.

Last edited by Aia; May 15th, 2009 at 11:01 am.