C++ , Vector & mysql

Question

I found this code from: http://www.davenicholas.me.uk/blog/view_post/29/How-to-c-mysql-mac-osx

#include <mysql.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>


#include <string>
#include <vector>

int main()
{

    std::vector<std::string> tables;
    MYSQL_RES *result;
    MYSQL_ROW row;
    MYSQL *connection, mysql;

    int state;

    connection = mysql_real_connect(&mysql,"localhost","username","password","database",0,0,0);

    if (connection == NULL)
    {
        std::cout << mysql_error(&mysql) << std::endl;

        return tables;
    }

    state = mysql_query(connection, "SHOW TABLES");
    if (state !=0)
    {
        std::cout << mysql_error(connection) << std::endl;
        return tables;
    }

    result = mysql_store_result(connection);

    std::cout << "tables: " << mysql_num_rows(result) << std::endl;
    while ( ( row=mysql_fetch_row(result)) != NULL )
    {
        tables.push_back(row[0]);
    }

    mysql_free_result(result);

    mysql_close(connection);
        return 0;
}

But when I build it I get the error:

error: cannot convert 'std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >' to 'int' in return

and

error: cannot convert 'std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >' to 'int' in return

`return tables;` main cannot return a `std::vector` to its caller — octal9, Mar 06 '12 at 16:31
Copy paste coding might work for languages like Java or PHP, but you are going to get destroyed if you try it in C++ — Swiss, Mar 06 '12 at 16:49
Im trying to connect to mysql and read the database using c++ — user1104856, Mar 07 '12 at 18:02
Before learning to connect to databases using C++, maybe you should learn using C++ first. — Sebastian Mach, Mar 08 '12 at 14:12

score 3 · Answer 1 · answered Mar 06 '12 at 16:32

3

I think the problem may be that you do return tables; when the connect or query calls fail. This means that you return a std::vector from main(), and main() should return an int.

answered Mar 06 '12 at 16:32

Weston

1,845
13
12

please give me example, or fix it... i want to pick the best answer – user1104856 Mar 07 '12 at 18:01

NPE · Answer 2 · 2012-03-06T16:48:48.450

1

Move this code into a function that returns std::vector<std::string>, and call that function from main():

std::vector<std::string> get_tables()
{
    std::vector<std::string> tables;
    MYSQL_RES *result;
    MYSQL_ROW row;
    MYSQL *connection, mysql;

    int state;

    connection = mysql_real_connect(&mysql,"localhost","username","password","database",0,0,0);

    ...

    return tables;
}

int main()
{
    std::vector<std::string> tables = get_tables();
    // do something useful with `tables'
    return 0;
}

edited Mar 06 '12 at 16:48

answered Mar 06 '12 at 16:27

NPE

486,780
108
951
1,012

4

@user1104856 You need to learn the very basics of the language before you can hope to understand or use that code, sorry. – Konrad Rudolph Mar 06 '12 at 16:33
It still dosent work: IT SAYS warning: control reaches end of non-void function – user1104856 Mar 06 '12 at 16:35
1

@user1104856: With respect, my recommendation at this juncture would be to pick up a good C++ textbook. See http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – NPE Mar 06 '12 at 16:41
I will, but i did try to return tables, it says: EXC_BAD_ACCESS – user1104856 Mar 06 '12 at 16:43

score 1 · Answer 3 · answered Mar 06 '12 at 16:30

1

This code is supposed to be in another function I think, definitely not in main().

answered Mar 06 '12 at 16:30

ebutusov

563
2
5

score 1 · Answer 4 · answered Mar 06 '12 at 17:45

1

That's because the table variable is defined as a vector, but it's returned as the function's return value; but the function is declared to have int as return value. The best way to solve this problem is to move the parts which process table to another function and call that from main (and rewrite some parts of the code).

answered Mar 06 '12 at 17:45

MMS

408
2
5
9

I try'd use the above code from aix, but i get : Program received signal: “EXC_BAD_ACCESS”. Could you please fix it? – user1104856 Mar 07 '12 at 01:09
I don't really know what the problem is, but I guess there is something wrong either with file access or mysql access. – MMS Mar 07 '12 at 15:04

C++ , Vector & mysql

4 Answers4