How to return a value from a pointer in C

I have the following code and I would like to return the value of 'out' and print it to a file. How do I return the value of 'out' instead of the location. Also, how do I call the function uint32_pack from the main function? Thank you for your help.

#if HAVE_PROTOBUF_C_CONFIG_H
#include "protobuf-c-config.h"
#endif
#include <stdio.h>                      /* for occasional printf()s */
#include <stdlib.h>                     /* for abort(), malloc() etc */
#include <string.h>                     /* for strlen(), memcpy(), memmove() */
#if HAVE_ALLOCA_H
#include <alloca.h>
#elif HAVE_MALLOC_H
#include <malloc.h>
#endif

#include "protobuf-c.h"

int main(void){
uint32_t hexvalue = 0x20;
int gnuvalue;
uint8_t fake_out;
  FILE *fp;

  fp = fopen("binarydata.txt","w");
  gn开发者_Python百科uvalue = uint32_pack (hexvalue, fake_out);
  fprintf(fp,"%x",gnuvalue);
  fclose(fp);
}


/* === pack() === */
/* Pack an unsigned 32-bit integer in base-128 encoding, and return the number of bytes needed:
   this will be 5 or less. */
static inline size_t
uint32_pack (uint32_t value, uint8_t *out)
{
  unsigned rv = 0;

  if (value >= 0x80)
    {
      out[rv++] = value | 0x80;
      value >>= 7;
      if (value >= 0x80)
        {
          out[rv++] = value | 0x80;
          value >>= 7;
          if (value >= 0x80)
            {
              out[rv++] = value | 0x80;
              value >>= 7;
              if (value >= 0x80)
                {
                  out[rv++] = value | 0x80;
                  value >>= 7;
                }
            }
        }

  /* assert: value<128 */
  out[rv++] = value;
  return &out;
  }
}

You want to dereference the pointer using the * unary operator, like so:

return *out;

Doing this, it'll return the value stored at the location pointed to by out.

There something odd in your code here

  uint8_t fake_out;
  gnuvalue = uint32_pack (hexvalue, fake_out);

while the prototype for uint32_pack needs uint8_t *, so it should be &fake_out. And then to return it, you need just to dereference the pointer to modify fake_out,something like *out = value;.

If you need to return two values (gnuvalue and fake_out), this is how you can.

Another option could be to return a pointer to a struct malloc-ed in the function (then you need to free it soon or later), and the struct holds both "gnuvalue" and "fake_out".

You should return *out. And update the comment to reflect this. In practice it seems like out should fit in a size_t (i.e. sizeof size_t will be large enough) but it is hack-ish to assume it.

On calling from main, the current way won't work because fake_out is an uint8_t, not an uint8_t*. Of course &fakeout will crash so don't do that, you have to allocate a large enough array of uint8_t.