mySQL query in C++

Question

I have the following code in my C++ program:

query_state = mysql_query(connection, "select * from cplpl");

if I want to replace the table name,cplpl, by a variable in my C++ program, how do I do it?

basically, I've created

string tblnm="cplpl";

but then if I run

query_state = mysql_query(connection, "select * from tblnm");

it looks for the table tblnm. I tried $tblnm also like you can do in Perl, but that doesn't work either

Is there a way I can fix this? thx!

EDIT: If I rewrite this as follows:

string tblnm="test";
string qrycd="select * from " +tblnm;
 query_state = mysql_query(connection, qrycd.c_str());

it works, however, if I want to add a where clause

string qrycd1="where fname like '%Bob%';";

and rewrite the code as

string qrycd="select * from " +tblnm +qrycd1;
 query_state = mysql_query(connection, qrycd.c_str());

I get an error..

of course you want to be careful if tblnm is user input and not just insert it into the query. See this question on parametirizing db names and table names in mysql: stackoverflow.com/questions/6656636/… — Doug T.
– Doug T., Commented Aug 23, 2011 at 17:35
You need to look into what C++ is and how it works. Its that simple. I recommend reading an introduction book — Martin Kristiansen
– Martin Kristiansen, Commented Aug 23, 2011 at 17:36

Eelke · Accepted Answer · 2011-08-23 17:33:32Z

8

This should work:

query_state = mysql_query(connection, ("select * from " + tblnm).c_str());

answered Aug 23, 2011 at 17:33

Eelke

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3 Comments

Seth Carnegie Over a year ago

+1 for being the only one to remember c_str() including myself.

Eelke Over a year ago

@itcplpl: when you do tblnm +qrycd1 you are missing whitespace between the tablename and the where keyword. When building queries dynamically allways take care to add spaces. Changing the code to tblnm + " " + qrycd1 should solve the issue. It will be a good debugging aid for yourself to output the query you create to standard out or a log so you can see what the actual query looks like. Then you would easily spot such problems yourself.

itcplpl Over a year ago

@Eelke, thanks very much for the constructive suggestion- I will do so. and yes, it worked :-)

Community · Accepted Answer · 2017-05-23 11:43:19Z

2

You can simply use operator+ of string:

query_state = mysql_query(connection, ("select * from " + tblnm).c_str());

You probably should read a good beginner's C++ book.

edited May 23, 2017 at 11:43

CommunityBot

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answered Aug 23, 2011 at 17:31

Seth Carnegie

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Comments

john · Accepted Answer · 2011-08-23 17:32:46Z

2

In C++ + is used for string concatenation.

string tblnm="cplpl";
query_state = mysql_query(connection, "select * from " + tblnm);

Don't try random things from other languages, read some C++ documentation.

answered Aug 23, 2011 at 17:32

john

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Martin Kristiansen · Accepted Answer · 2011-08-23 17:34:14Z

2

you need to construct the string.. look into this

http://www.cplusplus.com/reference/string/string/operator+=/

answered Aug 23, 2011 at 17:34

Martin Kristiansen

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1 Comment

Martin Kristiansen Over a year ago

look at @Seth_Carnegie's post

vromanov · Accepted Answer · 2011-08-23 22:02:37Z

0

Looks like you lost space after table name

string tblnm="cplpl ";

answered Aug 23, 2011 at 22:02

vromanov

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