Problem returning a string

**Schwarzhelm** · 10-15-2003

I keep having problems when I'm returning a string from my sub. It keeps printing:
CPU Type: Auth(????VB
CPU Model: AMD
when I print.

Here is my code:

Code:

char * GetCPUType()
{
    FILE* fp;
  char buffer[1024];
  size_t readBytes;
  char* CPUTypeMatch;
  char* CPUType;

  /* Read /proc/cpuinfo */
  fp = fopen ("/proc/cpuinfo", "r");
  readBytes = fread (buffer, 1, sizeof (buffer), fp);
  fclose(fp);

  /*quit if nothing is read */
  if(readBytes==0 || readBytes == sizeof(buffer))
    return EXIT_SUCCESS;
  buffer[readBytes] = '\0';

  /* Locate the CPU Type */
  CPUTypeMatch = strstr(buffer,"vendor_id");

  sscanf (CPUTypeMatch,"vendor_id : %s", &CPUType);
  
  return CPUType;

}

int main(int argc, char *argv[])
{
  char* CPUType;
  char* CPUModel;
  
  CPUType = GetCPUType();
  CPUModel = GetCPUModel();
  printf("CPU Type: %s \n", &CPUType);
  printf("CPU Model: %s \n", &CPUModel);

  return EXIT_SUCCESS;
}

Thank you!

**velius** · 10-15-2003

The pointer you are returning does not have a valid size set aside for the string. So you are printing valid data for some other process.

**Schwarzhelm** · 10-15-2003

Still no go.. I added a =malloc(100); in my code after the declarations. So my code in my main and bassically whereever else I had it written looks like this:

Code:

char* CPUType=malloc(100);

It still is printing out the same thing... any more help would be greatly appreciated. Thank you!

**velius** · 10-15-2003

Your pointer is pointing to nothing. You put the data in a different buffer.

**Schwarzhelm** · 10-15-2003

I'm sorry I guess I don't understand... could you please explain a little more..

thank you

**velius** · 10-15-2003

You are using sscanf(buffer, const char*, arg_list); You are using your inteded buffer in the arg_list position. Reverse the two char* variables.

**Schwarzhelm** · 10-15-2003

I don't think the sscanf is my problem. If I print directly from my Get sub it works fine, but I don't want to to that. I want the information to be printed from my Main.

**velius** · 10-15-2003

What I am telling you is the pointer to char (char*) you are returning is not in the recieving buffer position in the argument list past to sscanf(). You need to write it like this:

Code:

// your code is of which CPUType is not pointing to anything and
// you are then expecting a string or char array and then you are
// giving it the address of the pointer CPUType
sscanf (CPUTypeMatch,"vendor_id : %s", &CPUType);

// should be
sscanf (CPUType, "vendor_id : %s", CPUTypeMatch);

That should give you what you are looking to recieve. Just make sure that CPUType is pointing to a block of memory first.

**Schwarzhelm** · 10-15-2003

That still doesn't work ... and now it just prints
CPU Type: ???????VB

I think my sscanf order is fine... Like I said before it works fine if I print in my getCPUType sub, but when I try to return it to my main it does not display correctly. Furthermore, if I move all the code to my main and print it works fine, but I don't want to do that. I want to call this a few times just by calling the sub. Do you or anyone else have any other suggestions. I think my problem is with returning a string... or in C I guess it's a char pointer.

Thank you.

**swoopy** · 10-15-2003

> sscanf (CPUTypeMatch,"vendor_id : %s", &CPUType);
sscanf (CPUTypeMatch,"vendor_id : %s", CPUType);

> printf("CPU Type: %s \n", &CPUType);
printf("CPU Type: %s \n", CPUType);

**velius** · 10-16-2003

My prefered way to format a string would be to use sprintf() it workes just like printf only it writes to the buffer. It is much better to use that sscanf().

**quzah** · 10-16-2003

Originally posted by velius
My prefered way to format a string would be to use sprintf() it workes just like printf only it writes to the buffer. It is much better to use that sscanf().

sscanf and sprintf have entirely different uses. You cannot simply say one is better than the other. One reads from a buffer, the other writes to a buffer.

Quzah.

**Morgan** · 10-16-2003

You are completely misusing sscanf. This should be quite straightforward code. Try this...

Code:

#include <stdio.h>
#include <string.h>

char * get_word( void );

int main()
{
  char main_word[50];

  strcpy( main_word, get_word() );

  printf( "\n%s", main_word );

  sprintf( main_word, "Sub_word: %s'", get_word() );
  printf( "\n%s", main_word );

  printf( "\n%s\n\n", get_word() );

  return 0;
}

char *
get_word()
{
  char sub_word[50];

  strcpy( sub_word, "Easy" );

  return( sub_word );
}

**quzah** · 10-16-2003

Originally posted by Morgan
You are completely misusing sscanf. This should be quite straightforward code. Try this...

Code:

char * get_word() { char sub_word[50]; strcpy( sub_word, "Easy" ); return( sub_word ); }

You realize of course that you're returning the address of an array that goes out of scope when this function exits, right? As such, you end up pointing to an invalid memory location. Best to make it static, or use a pointer and malloc it.

Quzah.

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