Question_for_chap08mySQL

// page 352-353 of book Beginning Linux Programming , 4th edition 2007 
//The book is using the program of page 350 as a base , and expands on it slightly
//to reach the following , at page 352-353 :
//Here are some definitions , taken from the book and not from official MySQL C API 
//MYSQL *mysql_init(MYSQL *);  
//MYSQL *mysql_real_connect(MYSQL *connection,const char *server_host,const char*sql_user_name,const char *sql_password,
                            const char *db_name,unsigned int port_number,const char *unix_socket_name,unsigned int flags);  
//void mysql_close(MYSQL *connection);  
//MYSQL_ROW mysql_fetch_row(MYSQL_RES *result); 
//unsigned int mysql_errno(MYSQL *connection);  
//char *mysql_error(MYSQL *connection);  
//MYSQL_RES *mysql_use_result(MYSQL *connection);  
//unsigned int mysql_field_count(MYSQL *connection); 
//int mysql_query(MYSQL *connection, const char *query); 
// VERSION 1 , according to book 
#include <stdlib.h>
#include <stdio.h>
#include "mysql.h"
void display_row();
MYSQL my_connection; // use of 2 global variables , so they are easily accessed from function display()  
MYSQL_ROW sqlrow;
int main(void) 
{
    MYSQL_RES *res_ptr;
    int res;
    mysql_init(&my_connection);
    if (mysql_real_connect(&my_connection,"localhost","rick","secret","practicedb", 0, NULL, 0)) 
    {
        printf("Connection success\n");
        res = mysql_query(&my_connection,"SELECT childno, fname, age FROM children WHERE fname = 'Ann' ");
        if (res) { printf("SELECT error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
        else
         { 
            res_ptr = mysql_use_result(&my_connection);
            if (res_ptr) 
             {
                while ((sqlrow = mysql_fetch_row(res_ptr))) 
                   { 
                    printf("Fetched data , one row at a time ...\n"); 
                    display_row();
                   }
                if (mysql_errno(&my_connection)) 
                  { fprintf(stderr, "Retrive error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
                mysql_free_result(res_ptr);
             }
         }
        mysql_close(&my_connection);
     } 
    else 
     {
        fprintf(stderr, "Connection failed\n");
        if (mysql_errno(&my_connection)) 
         { fprintf(stderr,"Connection error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
     }
    return EXIT_SUCCESS;
}
void display_row()  //no need for parameters list
{
    unsigned int field_count;  /* number of columns */
    field_count = 0;
    while ( field_count < mysql_field_count(&my_connection) ) //global var my_connection is visible in here 
     {
        printf("%s ", sqlrow[field_count]);  //global var sqlrow is visible in here 
        field_count++;
     }
    printf("\n");
}
// gcc -I/usr/include/mysql select3globvar.c -L/usr/lib/mysql -lmysqlclient -o select3globvar 


// I implemented a variation of the above program , avoiding the local variables declaration 
// so I had to modify the definition and declaration of display( ...) 
//VERSION 2 , my alternate version , passing a pointer and a variable to the function  
#include <stdlib.h>
#include <stdio.h>
#include "mysql.h"
void display_row(MYSQL * some_connection_ptr , MYSQL_ROW dbrow);
int main(void) 
{
    MYSQL my_connection;
    MYSQL_RES *res_ptr;
    MYSQL_ROW sqlrow;
    int res;
    mysql_init(&my_connection);
    if (mysql_real_connect(&my_connection,"localhost","rick","secret","practicedb", 0, NULL, 0)) 
    {
        printf("Connection success\n");
        res = mysql_query(&my_connection,"SELECT childno, fname, age FROM children WHERE fname = 'Ann' ");
        if (res) { printf("SELECT error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
        else
         { 
            res_ptr = mysql_use_result(&my_connection);
            if (res_ptr) 
             {
                while ((sqlrow = mysql_fetch_row(res_ptr))) 
                   { 
                    printf("Fetched data , one row at a time ...\n"); 
                    display_row(&my_connection , sqlrow ); 
                   }
                if (mysql_errno(&my_connection)) 
                  { fprintf(stderr, "Retrive error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
                mysql_free_result(res_ptr);
             }
         }
        mysql_close(&my_connection);
     } 
    else 
     {
        fprintf(stderr, "Connection failed\n");
        if (mysql_errno(&my_connection)) 
         { fprintf(stderr,"Connection error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
     }
    return EXIT_SUCCESS;
}
void display_row(MYSQL * some_connection_ptr , MYSQL_ROW dbrow)
{
    unsigned int field_count;  /* number of columns */
    field_count = 0;
    while ( field_count < mysql_field_count(some_connection_ptr) )
     {
        printf("%s ", dbrow[field_count]);
        field_count++;
     }
    printf("\n");
}
// gcc -I/usr/include/mysql select3.c -L/usr/lib/mysql -lmysqlclient -o select3 



// This is another implementation with alternate display(...) definition and declaration 
// that does not uses pointers . Is it worse than the previous ?
// VERSION 3 
#include <stdlib.h>
#include <stdio.h>
#include "mysql.h"
void display_row(MYSQL  some_connection , MYSQL_ROW dbrow);
int main(void) 
{
    MYSQL my_connection;
    MYSQL_RES *res_ptr;
    MYSQL_ROW sqlrow;
    int res;
    mysql_init(&my_connection);
    if (mysql_real_connect(&my_connection,"localhost","rick","secret","practicedb", 0, NULL, 0)) 
    {
        printf("Connection success\n");
        res = mysql_query(&my_connection,"SELECT childno, fname, age FROM children WHERE fname = 'Ann' ");
        if (res) { printf("SELECT error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
        else
         { 
            res_ptr = mysql_use_result(&my_connection);
            if (res_ptr) 
             {
                while ((sqlrow = mysql_fetch_row(res_ptr))) 
                   { 
                    printf("Fetched data , one row at a time ...\n"); 
                    display_row(my_connection , sqlrow );
                   }
                if (mysql_errno(&my_connection)) 
                  { fprintf(stderr, "Retrive error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
                mysql_free_result(res_ptr);
             }
         }
        mysql_close(&my_connection);
     } 
    else 
     {
        fprintf(stderr, "Connection failed\n");
        if (mysql_errno(&my_connection)) 
         { fprintf(stderr,"Connection error %d: %s\n",mysql_errno(&my_connection), mysql_error(&my_connection)); }
     }
    return EXIT_SUCCESS;
}
void display_row(MYSQL some_connection , MYSQL_ROW dbrow)
{
    unsigned int field_count;  /* number of columns */
    field_count = 0;
    while ( field_count < mysql_field_count(&some_connection) ) 
     {
        printf("%s ", dbrow[field_count]);
        field_count++;
     }
    printf("\n");
}
// gcc -I/usr/include/mysql select3.c -L/usr/lib/mysql -lmysqlclient -o select3