Calling into C code

I think your third parameter should be szName rather than &szName. The API is asking for a pointer to a buffer. You are supplying it a pointer to a pointer to a buffer.

 

1. Please show the type of the variable hdbc. If its type is SQLHDBC, then your first function arg is wrong. The declared type is

Code:

SQLHDBC ConnectionHandle

not

Code:

SQLHDBC * ConnectionHandle

There should have been a compiler warning about mismatched types. If not, you should turn on strict arg-type checking for functions, and pay attention to all warnings.


2. If nResult isn't successful, does the block return or otherwise break sequential flow? Because if it doesn't, it will fall thru to NSString stringWithCString:, which I'm pretty sure won't work.


3. Is the string data really in the ASCII encoding? ASCII is a 7-bit code. If there are any bytes in the range 0x80-0xFF, it ain't ASCII.

 

stringWithCString:encoding: is declared as:

Code:

+ (id)stringWithCString:(const char *)cString encoding:(NSStringEncoding)enc

So why are you passing

Code:

&szName

Which you are casting to be a char*? What does the & operator do? Does this result in a pointer? Or did you already have a pointer before you used the & operator (hint are arrays really pointers)?

 

@ ScoobyMcDoo & robbieduncan

Code:

#include <stdio.h>

#define SQL_MAXIMUM_CATALOG_NAME_LENGTH  20

typedef  unsigned char  SQLCHAR;

int main( int argc, const char * argv[] )
{
	SQLCHAR szName[ SQL_MAXIMUM_CATALOG_NAME_LENGTH ];
	int nums[ 10 ];

	printf( " szName: %p\n", szName );
	printf( " &szName: %p\n", &szName );
	printf( " &szName[0]: %p\n", &szName[0] );

	printf( " nums: %p\n", nums );
	printf( " &nums: %p\n", &nums );
	printf( " &nums[0]: %p\n", &nums[0] );
}

Output (64-bit):

Code:

 szName: 0x7fff5fbff890
 &szName: 0x7fff5fbff890
 &szName[0]: 0x7fff5fbff890
 nums: 0x7fff5fbff860
 &nums: 0x7fff5fbff860
 &nums[0]: 0x7fff5fbff860

In C, the unadorned name of an array is a constant pointer to the first element of that array. Since it's a constant, it can't have its address taken (prefix & operator). The compiler simply gives the address of the first array element, effectively ignoring the &. There was a time when C compilers complained about & prefixing array names, but that was long, long ago.

If szName were declared as pointer type, then it can have its address taken. The code illustrating this is left as an exercise for the reader.

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Glad it worked out.

Your OS version? Xcode version? Development tools (Xcode, make, something else)?

-Wall should turn on most warnings. Otherwise consult the man page for gcc and look for the word prototype.

 

Wow, I forgot all about that. Made me curious, so I looked it up in my trusty 1st edition K&R and sure enough is says that taking the address of an array is illegal.