Question

I’m having troubles when calling a function taking a pointer to a string as a parameter. I need to get an Element’s name.

// method
void getStringFromCsv( char ** str );

Let me introduce the structures I’m working with (not written by me and part of a much bigger project, I can’t modify them).

// typedefs
typedef char      T_CHAR64[64];
typedef T_CHAR64  T_SYMBOL;

// generic element
typedef struct Element
{
  T_SYMBOL  name; 
} T_Element;

// csv element
typedef struct CsvElement
{
  Element * pElement;
  int   id;
} T_csvElement;

So, basically, I thought I would call the function like this :

T_Element * pData; // Not null, filled earlier
getStringFromCsv( &pData->pElement->name );

But this doesn’t work (warning: passing argument 1 of ‘STR_toCsv’ from incompatible pointer type). I’m using gcc with NetBeans 6.8.

I tried many things…

T_SYMBOL foo = "foo";
T_SYMBOL * pFoo = &foo;

getStringFromCsv( pDef->name, &pFoo ); // error : passing from incompatible pointer type

T_CHAR * pBar = &foo;      // error : init from incompatible pointer type
T_CHAR * pBaz = &(foo[0]); // OK

getStringFromCsv( pDef->name, &pBaz ); // OK

T_SYMBOL * pFooTest = &(foo[0]); // error : init from incompatible pointer type

…but ended up casting name to a char ** :

getStringFromCsv( (char**) &pData->pElement->name );

What is wrong with my code ?
Basically, SYMBOL = CHAR *, right ? Why is SYMBOL* != CHAR** ?
I’m pretty sure I’m missing something simple but right now… Nothing came.

EDIT
Here is getStringFromCsv :

void getStringFromCsv( char ** data )
{
  // pDesc is defined and not null
  csvDescriptorCat( pDesc, *data);
  csvDescriptorCat( pDesc, "\t");
}

void csvDescriptorCat( CsvDescriptor * pDesc, char* str)
{
  int len;
  if( str != NULL)
  {
    len = strlen(str);
    strcpy( &pDesc->line[pDesc->pos], str);
    pDesc->pos += len;
  }
}

Answer 1

If you wish to pass &pData->pElement->name to the function, the function must be declared as:

void getStringFromCsv(T_SYMBOL * str);

Alternatively you can use a temporary char * as Secure offered – but there’s not much point in doing this, because any updates to that char *‘s value can’t be used – the ->name member can’t be modified, as it’s an array.

You might as well just declare the function as:

void getStringFromCsv( char * str );

…and call it as:

getStringFromCsv( pData->pElement->name );

(In this case, the function can still change the contents of the ->name array. What you can’t do is to change the position of the array itself).

---

As well as Secure’s option, there’s another way if your compiler supports C99 compound literals:

getStringFromCsv( &(char *){ pData->pElement->name } );