Basic pointers to structures question...

**superbbrr** · 05-16-2012

header:

Code:

struct termlist
{
      uint32_t num_terms; 
      char **term;           
};

int getMetaData( uint32_t specific_tag, termlist **terms);

main:

Code:

int main(int argc, char **argv)
{

uint32_t specificTag;
specificTag = atoi(argv[1]);

termlist *sample1;

getMetaData( specificTag, sample1 );

...

}

Hi, I'm really confused about pointers to structures. I'm trying to understand this snippet of code above.

The function prototype requires a double pointer to the structure, termlist **terms. But in main when calling the function only a pointer to the structure is passed, sample1.

I'm quite confused on how the function prototype requires a double pointer, but in main only a single pointer is passed.

Thanks!

**ZuK** · 05-16-2012

Originally Posted by superbbrr

I'm quite confused on how the function prototype requires a double pointer, but in main only a single pointer is passed.

I'd be confused too if that would compile

Kurt

**cas** · 05-16-2012

First, either you're using a C++ compiler or you've omitted a typedef for your struct. If you're writing C, don't use a C++ compiler.

A compiler is required to spit out some sort of diagnostic for that code, because you're converting between incompatible pointer types. Is your compiler giving you a warning? If so, heed it! If not, either your compiler is very bad or you're not compiling the code you showed here.

**HowardL** · 05-16-2012

You should always check argc before trying to access argv[1] or greater and then qualify that value before using, otherwise your program might blow up your computer.

Re:

Code:

    termlist *sample1;

The declaration shows no datatype.
"termlist" is not a data type. It is an identifier of type ??????.

Are you sure you want a pointer?
If you are new structs and all perhaps you should start with a termlist object itself.

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