MySQL Connector/C++
MySQL connector library for C and C++ applications
Connector/C++ 8.0 X DevAPI for C Reference

Connector/C++ implements a variant of X DevAPI that can be used by applications written in plain C - the X DevAPI for C. It allows one to work with MySQL Servers implementing a document store via the X Plugin. One can also execute plain SQL queries using this API.

To get started, check out some of the main X DevAPI for C functions:

  • To access data first create a session using one of mysqlx_get_session_xxx() functions. These functions return a pointer to an opaque session handle of type mysqlx_session_t.
  • To work with documents in a collection or rows in a table, create a handle to the collection or the table using the mysqlx_get_collection() or the mysqlx_get_table() function. One first needs to obtain a schema handle with the mysqlx_get_schema() function.
  • Given a handle to a collection or a table object, one can execute queries and statements on that object directly, using functions like mysqlx_collection_find(), or one can create a statement handle with a function like mysqlx_collection_find_new() and execute it later with mysqlx_execute() after specifying additional statement parameters.
  • Collection or table statements can use named parameters. Values of these parameters must be defined using mysqlx_stmt_bind() before statement is executed.
  • To execute SQL, use the function mysqlx_sql(). SQL queries can contain ? placeholders whose values need to be specified either with mysqlx_stmt_bind(), prior to query execution, or directly in the function mysqlx_sql_param() which executes such a query.
  • Executing a statement produces a result handle of type mysqlx_result_t. It can be used to fetch result's data with functions mysqlx_row_fetch_one() or mysqlx_json_fetch_one(). It can be also used to examine the result metadata (in case of results of table queries) with the mysqlx_column_get_xxx family of functions.
  • Documents are represented as JSON strings. When getting data from rows with mysqlx_get_xxx() functions, conversion from database types to the indicated C native type is performed. Both types must match, otherwise result might be corrupted (there are no automatic type conversions). It is also possible to get raw bytes representing the value using the mysqlx_get_bytes() function.
  • Data items are fetched from the result one-by-one without storing complete result in memory. It is however possible to buffer a complete result with the mysqlx_store_result() function.

Many functions in X DevAPI for C have a variable parameters list allowing passing arguments in a flexible way. A good illustration of this approach is binding values to ? placeholders in an SQL query. The function mysqlx_stmt_bind() can bind the corresponding values to all parameters in just one call. For example:

mysqlx_stmt_bind(stmt, PARAM_SINT(v_sint),
PARAM_UINT(v_uint),
PARAM_FLOAT(v_float),
PARAM_DOUBLE(v_double),
PARAM_STRING(v_str),
PARAM_END);

There are several things to keep in mind:

  • In order to be able to correctly recognize the native parameter type in the parameter list each parameter must carry the type information. This is done using PARAM_TTT() macros. It is important to use the correct macro for each type such as PARAM_DOUBLE(v_double) can only be used if v_double is declared to have type double or PARAM_STRING(v_str) can only be used on v_str declared as char*.
  • The variable parameters functions in C do not have the means to know the exact number of given parameters on their own. Therefore, it is the caller's responsibility to put PARAM_END as the last parameter and in this way mark the end of the variable parameters list. Failure to do so cannot be detected at the build time, but it will most likely result in an abnormal program termination.

A more complete example of code that access MySQL Database using the X DevAPI for C is presented below. See also the list of X DevAPI for C Functions.

Sample code which uses Connector/C++ with X DevAPI for C

The following plain C application uses X DevAPI for C to connect to a MySQL Server with X Plugin, create a table, add a few rows into it using different ways such as plain SQL with parameters and table INSERT statements. Next, the code reads the table rows and displays the result.

The sample code can be found in file testapp/xapi_test.cc in the source distribution of Connector/C++ 8.0. See Using Connector/C++ 8.0 for instructions on how to build the sample code.

Code which uses the Connector/C++ X DevAPI for C should include the mysqlx/xapi.h header.

#include <mysqlx/xapi.h>
The main header for MySQL Connector/C++ X DevAPI for C.

Checking for errors is an essential part of any program, but in this sample code it can take too much space, therefore we introduce the convenience macros that check for statement errors, result errors and general errors:

/* Error processing macros */
#define CRUD_CHECK(C, S) if (!C) \
{ \
printf("\nError! %s", mysqlx_error_message(S)); \
return -1; \
}
#define RESULT_CHECK(R, C) if (!R) \
{ \
printf("\nError! %s", mysqlx_error_message(C)); \
return -1; \
}
#define IS_OK(R, C) if (R != RESULT_OK) \
{ \
printf("\nError! %s", mysqlx_error_message(C)); \
return -1; \
}
#ifdef _WIN32

Start with creating a session handle using one of the mysqlx_get_session_xxx() functions. Session parameters are specified within mysqlx connection string. In this case connection string specifies a session on the local host as user root. Alternative connection string can be given as command line argument.

If session could not be established, mysqlx_get_session_from_url() returns NULL handle while error message and code are stored in provided buffers.

const char *url = (argc > 1 ? argv[1] : "mysqlx://root@127.0.0.1");

Once created, the session is ready to be used. If the session cannot be established the program prints the error and exits.

Use the session to execute SQL queries – here we create a test table. After executing a query, we check its status with the RESULT_CHECK() macro (which checks if returned result handle is not NULL).

Note
If a query is a null-terminated string the query length parameter can be MYSQLX_NULL_TERMINATED, in which case query length is determined by the function.

The plain SQL queries executed before did not have any parameters. Next thing to do is to execute an SQL insert statement with ? placeholders. One way of doing this is to first create a statement handle with mysqlx_sql_new(). Such statement is not executed right away – it will be executed later, after binding the placeholder values first.

The placeholder values for the above statement are specified through a call to the mysqlx_stmt_bind() function. Parameters list consists of <type, value> pairs. We use convenience macros PARAM_TTT() to generate such pairs. The list of placeholder values is terminated with PARAM_END.

Note
The type identifier of the parameter must correspond to the actual C type of the value. Otherwise the parameters stack might be corrupted. For instance MYSQLX_TYPE_SINT indicates that the next parameter will have the type of signed 64-bit integer (in this case v_sint declared as int64_t).

Once the placeholder values are specified, the statement can be executed with mysqlx_execute(). Attempt to execute statement with placeholders, without binding values to these placeholders will result in an error. Similar, if the number of bound values is less than the number of placeholders, the attempt to execute such a statement will result in an error. The fact that all placeholders are bound to values is checked only when the statement is executed, not when binding the values.

For the purpose of demonstration we will insert the next row using a specialized table INSERT statement. First, get a handle to the table object with mysqlx_get_schema() and mysqlx_get_table() functions. The third parameter to these functions is a Boolean flag specifying if an error should be reported if indicated objects do not exist in the database. Without such a check it is possible to create a handle to a non-existing object but then the handle creation is cheap and does not involve any communication with the database. Errors would be reported later, when one attempts to execute a statement for such a non-existent handle.

Create a table INSERT statement using mysqlx_table_insert_new().

The next step is to provide the row data using the mysqlx_set_insert_row() function, which can be called multiple times on the same statement handle before the statement is executed. In this way a multi-row insert will be performed.

In our example we will do a single-row insert. Same as in case of mysqlx_stmt_bind() the row data is specified as <type, value> pairs and the list of function parameters is terminated by PARAM_END. After specifying the row data, the insert statement is executed:

After the inserts are finished the code will read the rows. To do so execute table SELECT statement with mysqlx_table_select_limit(). This limits the number of returned rows to 500:

Note that mysqlx_table_select_limit() executes the statement right away, returning its result. Before we were first creating a statement handle, then adding information to the statement and then executing it.

Now fetch rows one by one. Function mysqlx_row_fetch_one() returns NULL handle when there are no more rows in the result:

The actual data is read using mysqlx_get_xxx() functions. These functions return the values through the output parameters.

Along with the data the code can get metadata such as the column names. In this example we just print the column name returned by mysqlx_column_get_name():

Close the session using mysqlx_session_close(). This implicitly frees all handles associated with the session (results, rows, etc):

The complete code of the example is presented below:

/*
* Copyright (c) 2016, 2019, Oracle and/or its affiliates. All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License, version 2.0, as
* published by the Free Software Foundation.
*
* This program is also distributed with certain software (including
* but not limited to OpenSSL) that is licensed under separate terms,
* as designated in a particular file or component or in included license
* documentation. The authors of MySQL hereby grant you an
* additional permission to link the program and your derivative works
* with the separately licensed software that they have included with
* MySQL.
*
* Without limiting anything contained in the foregoing, this file,
* which is part of MySQL Connector/C++, is also subject to the
* Universal FOSS Exception, version 1.0, a copy of which can be found at
* http://oss.oracle.com/licenses/universal-foss-exception.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU General Public License, version 2.0, for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdio.h>
#include <mysqlx/xapi.h>
#include <string.h>
/* Error processing macros */
#define CRUD_CHECK(C, S) if (!C) \
{ \
printf("\nError! %s", mysqlx_error_message(S)); \
return -1; \
}
#define RESULT_CHECK(R, C) if (!R) \
{ \
printf("\nError! %s", mysqlx_error_message(C)); \
return -1; \
}
#define IS_OK(R, C) if (R != RESULT_OK) \
{ \
printf("\nError! %s", mysqlx_error_message(C)); \
return -1; \
}
#ifdef _WIN32
#define format_64 "[%s: %I64d] "
#else
#define format_64 "[%s: %lld] "
#endif
int main(int argc, const char* argv[])
{
const char *url = (argc > 1 ? argv[1] : "mysqlx://root@127.0.0.1");
int64_t v_sint = -17;
uint64_t v_uint = 101;
float v_float = 3.31f;
double v_double = 1.7E+08;
const char *v_str = "just some text";
int rc = 0;
int row_num = 0;
/*
Connect and create session.
*/
sess = mysqlx_get_session_from_url(url, &error);
if (!sess)
{
printf("\nError! %s. Error Code: %d", mysqlx_error_message(error),
mysqlx_free(error);
return -1;
}
printf("\nConnected...");
{
/*
TODO: Only working with server version 8
*/
res = mysqlx_sql(sess,
"show variables like 'version'",
MYSQLX_NULL_TERMINATED);
size_t len=1024;
char buffer[1024];
if (RESULT_OK != mysqlx_get_bytes(row, 1, 0, buffer, &len))
return -1;
int major_version;
major_version = atoi(buffer);
if (major_version < 8)
{
printf("\nSession closed");
return 0;
}
}
/* Drop test table if exists */
res = mysqlx_sql(sess,
"DROP TABLE IF EXISTS test.crud_placeholder_test",
MYSQLX_NULL_TERMINATED);
RESULT_CHECK(res, sess);
/* Create a test table */
res = mysqlx_sql(sess,
"CREATE TABLE test.crud_placeholder_test " \
"(sint BIGINT, uint BIGINT UNSIGNED, flv FLOAT," \
"dbv DOUBLE, strv VARCHAR(255))",
MYSQLX_NULL_TERMINATED);
RESULT_CHECK(res, sess);
printf("\nTable created...");
/* Do insert as a plain SQL with parameters */
crud = mysqlx_sql_new(sess,
"INSERT INTO test.crud_placeholder_test " \
"(sint, uint, flv, dbv, strv) VALUES (?,?,?,?,?)",
MYSQLX_NULL_TERMINATED);
CRUD_CHECK(crud, sess);
/* Provide the parameter values */
rc = mysqlx_stmt_bind(crud, PARAM_SINT(v_sint),
PARAM_UINT(v_uint),
PARAM_FLOAT(v_float),
PARAM_DOUBLE(v_double),
PARAM_STRING(v_str),
PARAM_END);
IS_OK(rc, crud);
/* Execute the query */
res = mysqlx_execute(crud);
RESULT_CHECK(res, crud);
/*
Query table using CRUD operations.
*/
db = mysqlx_get_schema(sess, "test", 1);
RESULT_CHECK(db, sess);
table = mysqlx_get_table(db, "crud_placeholder_test", 1);
RESULT_CHECK(table, db);
crud = mysqlx_table_insert_new(table);
/* Change values to have some differences in inserted rows */
v_sint = -232;
v_uint = 789;
v_float = 99.34f;
v_double = 2.84532E-5;
v_str = "some more text";
rc = mysqlx_set_insert_row(crud, PARAM_SINT(v_sint),
PARAM_UINT(v_uint),
PARAM_FLOAT(v_float),
PARAM_DOUBLE(v_double),
PARAM_STRING(v_str),
PARAM_END);
IS_OK(rc, crud);
/* Execute the query */
res = mysqlx_execute(crud);
RESULT_CHECK(res, crud);
printf("\nRows inserted...");
/* Read the rows we have just inserted, limit to 500 rows, no sorting. */
"(sint < 10) AND (UINT > 100)", 500, 0, PARAM_END);
RESULT_CHECK(res, table);
printf("\n\nReading Rows:");
while ((row = mysqlx_row_fetch_one(res)))
{
int64_t v_sint2 = 0;
uint64_t v_uint2 = 0;
float v_float2 = 0;
double v_double2 = 0;
char v_str2[256];
const char *col_name;
size_t buf_len = sizeof(v_str2);
printf("\nRow # %d: ", ++row_num);
IS_OK(mysqlx_get_sint(row, 0, &v_sint2), crud);
col_name = mysqlx_column_get_name(res, 0);
printf(format_64, col_name, (long long int)v_sint2);
IS_OK(mysqlx_get_uint(row, 1, &v_uint2), crud);
col_name = mysqlx_column_get_name(res, 1);
printf(format_64, col_name, (long long int)v_uint2);
IS_OK(mysqlx_get_float(row, 2, &v_float2), crud);
col_name = mysqlx_column_get_name(res, 2);
printf("[%s: %f]", col_name, v_float2);
IS_OK(mysqlx_get_double(row, 3, &v_double2), crud);
col_name = mysqlx_column_get_name(res, 3);
printf("[%s: %f]", col_name, v_double2);
IS_OK(mysqlx_get_bytes(row, 4, 0, v_str2, &buf_len), crud);
col_name = mysqlx_column_get_name(res, 4);
printf("[%s: %s [%u bytes]]", col_name, v_str2, (unsigned)buf_len);
}
printf("\nSession closed");
return 0;
}
unsigned int mysqlx_error_num(void *obj)
Get the error number from the object.
const char * mysqlx_error_message(void *obj)
Get the error message from the object.
const char * mysqlx_column_get_name(mysqlx_result_t *res, uint32_t pos)
Get column name.
int mysqlx_get_float(mysqlx_row_t *row, uint32_t col, float *val)
Get a float number from a row.
int mysqlx_get_uint(mysqlx_row_t *row, uint32_t col, uint64_t *val)
Get an unsigned integer number from a row.
int mysqlx_get_bytes(mysqlx_row_t *row, uint32_t col, uint64_t offset, void *buf, size_t *buf_len)
Read bytes stored in a row into a pre-allocated buffer.
int mysqlx_get_double(mysqlx_row_t *row, uint32_t col, double *val)
Get a double number from a row.
mysqlx_row_t * mysqlx_row_fetch_one(mysqlx_result_t *res)
Fetch one row from the result.
int mysqlx_get_sint(mysqlx_row_t *row, uint32_t col, int64_t *val)
Get a signed integer number from a row.
mysqlx_schema_t * mysqlx_get_schema(mysqlx_session_t *sess, const char *schema_name, unsigned int check)
Get a schema object and optionally check if it exists on the server.
void mysqlx_session_close(mysqlx_session_t *session)
Close the session.
mysqlx_session_t * mysqlx_get_session_from_url(const char *conn_string, mysqlx_error_t **error)
Create a session using connection string or URL.
mysqlx_table_t * mysqlx_get_table(mysqlx_schema_t *schema, const char *tab_name, unsigned int check)
Get a table object and optionally check if it exists in the schema.
mysqlx_result_t * mysqlx_sql(mysqlx_session_t *sess, const char *query, size_t query_len)
Execute a plain SQL query.
mysqlx_stmt_t * mysqlx_sql_new(mysqlx_session_t *sess, const char *query, uint32_t length)
Create a statement which executes a plain SQL query.
int mysqlx_stmt_bind(mysqlx_stmt_t *stmt,...)
Bind values for parametrized statements.
int mysqlx_set_insert_row(mysqlx_stmt_t *stmt,...)
Specify a row to be added by an INSERT statement.
void mysqlx_free(void *obj)
Free the allocated handle explicitly.
mysqlx_result_t * mysqlx_execute(mysqlx_stmt_t *stmt)
Execute a statement.
mysqlx_stmt_t * mysqlx_table_insert_new(mysqlx_table_t *table)
Create a statement executing a table INSERT operation.
mysqlx_result_t * mysqlx_table_select_limit(mysqlx_table_t *table, const char *criteria, uint64_t row_count, uint64_t offset,...)
Execute a table SELECT statement with a WHERE, ORDER BY and LIMIT clauses.
#define RESULT_OK
Return value indicating function/operation success.
Definition: xapi.h:103
struct mysqlx_result_struct mysqlx_result_t
Type of result handles.
Definition: xapi.h:301
struct mysqlx_row_struct mysqlx_row_t
Type of row handles.
Definition: xapi.h:288
struct mysqlx_stmt_struct mysqlx_stmt_t
Type of statement handles.
Definition: xapi.h:277
struct mysqlx_session_struct mysqlx_session_t
Type of session handles.
Definition: xapi.h:205
struct mysqlx_error_struct mysqlx_error_t
Type of error handles.
Definition: xapi.h:196
struct mysqlx_schema_struct mysqlx_schema_t
Type of database schema handles.
Definition: xapi.h:244
struct mysqlx_table_struct mysqlx_table_t
Type of table handles.
Definition: xapi.h:261

A sample output produced by this code:

Connected...
Table created...
Rows inserted...
Reading Rows:
Row # 1: [sint: -17] [uint: 101] [flv: 3.310000][dbv: 170000000.000000][strv: just some text [15 bytes]]
Row # 2: [sint: -232] [uint: 789] [flv: 99.339996][dbv: 0.000028][strv: some more text [15 bytes]]
Session closed