Database Reference
In-Depth Information
If the API program has connected to MySQL, it can query the MySQL server with a query
function suchas
mysql_query()
. Let's use
SELECT
to get a list of birds from the
birds
table. The code for doing this and displaying the results is as follows:
...
if
(
mysql_query
(
mysql
,
"SELECT common_name, scientific_name FROM
birds"
)) {
fprintf
(
stderr
,
"%d: %s
\n
"
,
mysql_errno
(
mysql
),
mysql_error
(
mysql
));
}
else
{
result
=
mysql_store_result
(
mysql
);
while
(
row
=
mysql_fetch_row
(
result
)){
printf
(
"\%s - \%s
\n
"
,
row
[
0
],
row
[
1
]);
}
mysql_free_result
(
result
);
}
mysql_close
(
mysql
);
return
0
;
}
Within the
if
statement here, we're using
mysql_query()
to query MySQL. You
could use the
mysql_real_query()
functioninstead. It allows the retrieval of binary
data, which can be safer, but isn't necessary for this simple example. The
mysql_query()
function returns 0 if it's successful and nonzero if it's not. So if the
SQL statement contained within it doesn't succeed in selecting data from MySQL, an er-
ror message will be printed. However, if the query is successful, the
else
statement will
then be executed, because the
if
statement will have received a value of 0.
In the
else
statement block, the first line usesthe
mysql_store_result()
function
to store the results of the query in the
result
variable.
Before letting go of the data, using
while
, the code loops through each row of the results
set. We're usingthe
mysql_fetch_row()
function to fetch each row and store it tem-
porarily in the
row
variable. Because we know how the data is organized from the
SELECT
statement, we can use
printf
with its formatting codes to display each
column. Notice that each column is extracted with standard array syntax (i.e.,
array
[
n
]
).
Once C has gone through each row of the results, it will stop processing and use
mysql_free_result()
to freethe memory for
result
, concluding the
else
state-
ment.
