Question

I’m passing a pointer to a pointer (**resultSet) to my MySQL function.

Here’s an excerpt on how I copy the MySQL data from within the function:

int
getItems(char * cmd, char **resultSet)
{

...
MYSQL initialisations and set-up
...



    resultSet = malloc(sizeof(char)*(int)mysql_num_rows);

    while((row = mysql_fetch_row(result))) 
    {

            for (i=0 ; i < mysql_num_fields(result); i++)               
            {   
            printf("%i: \t", i);        
            resultSet[counter] = malloc(sizeof(char)*strlen(row[i])+1);
            strcpy(resultSet[counter], row[i]);
            printf("%s\n", resultSet[counter]);
            }
            printf("---------------------\n");
            counter++;      
    }
...
MYSQL cleaning up
...
return 0;
}

Calling it in main with

getItems(cmd, resultSet);

From within my getItems function this

printf("%s\n", resultSet[0]);

seems to work.

However, if I try to access it from outside my function I get a segmentation fault. Why is this?

Answer 1

If you want to use resultSet as a return parameter, you need to make the function signature

int getItems(char * cmd, char ***resultSet)

and use it in the function like

*resultSet = malloc(sizeof(char)*(int)mysql_num_rows)

The function call could look like

char** results;
nitems = getItems(somecmd, &results); 

Better and simpler is probably to leave it as it is and make the allocation before the function call.