Embedded MariaDB C/C++ API

Question

I'm trying to get an embedded MariaDB (i.e. not connecting to running server) setup going but I'm failing to get any of the examples I find to work.

The most recent example I have is from this post https://stackoverflow.com/a/24548826/400048

When the app runs it produces: Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2) The docs https://mariadb.com/kb/en/library/embedded-mariadb-interface/ isn't much help on this.

For convenience the code from that StackOverflow post is:

#include <my_global.h>
#include <mysql.h>

int main(int argc, char **argv) {  
    static char *server_options[] = {
                                   "mysql_test", // An unused string 
                                    "--datadir=/tmp/mysql_embedded_data", // Your data dir
                                    NULL };
    int num_elements = (sizeof(server_options) / sizeof(char *)) - 1;

    static char *server_groups[] = { "libmysqld_server",
                                     "libmysqld_client", NULL };


    // Init MySQL lib and connection    
    mysql_library_init(num_elements, server_options, server_groups);
    MYSQL *con = mysql_init(NULL);

    if (con == NULL) {
        fprintf(stderr, "%s\n", mysql_error(con));
        exit(1);
    }

    mysql_options(con, MYSQL_READ_DEFAULT_GROUP, "libmysqld_client");
    mysql_options(con, MYSQL_OPT_USE_EMBEDDED_CONNECTION, NULL);

    // Connect to no host/port -> Embedded mode
    if (mysql_real_connect(con, NULL, NULL, NULL, NULL, 0, NULL, 0) == NULL) {
        fprintf(stderr, "%s\n", mysql_error(con));
        mysql_close(con);
        exit(1);
    }

    // Create a sample empty DB, named "aNewDatabase"
    if (mysql_query(con, "CREATE DATABASE aNewDatabase")) {
        fprintf(stderr, "%s\n", mysql_error(con));
        mysql_close(con);
        exit(1);
    }

    // Close connection
    mysql_close(con);
    exit(0);
}

I had a cursory look at https://github.com/MariaDB/server but didn't know where to really look...or in fact what I was looking for. How does one go about getting an embedded mariadb going? I'm running on Mac OS High Sierra, MariaDB was installed with brew install mariadb --with-embedded.

UPDATE:

I'm fairly certain I'm linking to the correct lib.

ls /usr/local/lib | grep maria

FIND_LIBRARY(mariadb mariadb)
MESSAGE(FATAL_ERROR "BOOM ${mariadb}")

Output of which is: BOOM /usr/local/lib/libmariadb.dylib

UPDATE 2

I'm now linking to the following. Note that I started with just libmysqld and added libraries until all link errors went away. The trouble here is I may not have all the correct libs or versions.

TARGET_LINK_LIBRARIES(sql_fn /usr/local/lib/libmysqld.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/opt/openssl/lib/libcrypto.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/opt/openssl/lib/libssl.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/opt/bzip2/lib/libbz2.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/lib/liblz4.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/opt/zlib/lib/libz.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/opt/xz/lib/liblzma.a)
TARGET_LINK_LIBRARIES(sql_fn /usr/local/lib/libsnappy.a)

It now compiles but exits with code 6

Process finished with exit code 6 Looking at https://stackoverflow.com/a/7495907/400048 if it's points to the same thing/is still true then exit code 6 means EX_ILLEGAL_TABLE 6, unfortunately I don't know what table that would be. The mysql_test and datadir strings passed in are valid identifiers/path.

Answer 1

Ok first a little explanation about your example. The user is using gcc to compile and I can see you are using cmake. First what does -lz and mysql_config --include --libmysqld-libs means. The first is link zlib to link zlib in cmake you can refer to this answer, but long story short:

find_package( ZLIB REQUIRED )
if ( ZLIB_FOUND )
    include_directories( ${ZLIB_INCLUDE_DIRS} )
    target_link_libraries( sql_fn ${ZLIB_LIBRARIES} )
endif( ZLIB_FOUND )

Then you need the mariaDB library and that is the second part. mysql_config --include --libmysqld-libs this means execute the command mysql_config --include --libmysqld-libs which will return a string with the link options so execute the command:

$mysql_config --include --libmysqld-libs
-I/usr/local/mysql/include
-L/usr/local/mysql/lib  -lmysqld

And you should get an output like the one above. The -I is to look for headers in a given directory and the -L is to search a library in a directory, the -l is to link a given library it serves the same purpose as -lz only you are adding -lmysqld.

Well now that all is explained you need only include the -I -L and -l options with mysql however this is not such a standard library so you need to include directories and libraries through a script as explained in this anwer. So again long story short there is no bullet proof for this for example my library is in /usr/local/mysql/lib and yours is in /usr/local/lib. Since that is the case it will be easier to use the second method.

execute_process(COMMAND mysql_config --include
    OUTPUT_VARIABLE MYSQL_INCLUDE)
execute_process(COMMAND mysql_config --libmysqld-libs
    OUTPUT_VARIABLE MYSQL_LIBS)

target_compile_options(sql_fn PUBLIC ${MYSQL_INCLUDE})
target_link_libraries(sql_fn ${MYSQL_LIBS})

And that is all the required information you need. Now we are glad we have Cmake to make things easier for us don't we. ;) Here is my CMakeLists.txt

cmake_minimum_required(VERSION 3.6)
project(embedded_mysql)

set(CMAKE_CXX_STANDARD 14)

set(SOURCE_FILES main.cpp)
add_executable(embedded_mysql ${SOURCE_FILES})

find_package( ZLIB REQUIRED )
if ( ZLIB_FOUND )
    include_directories( ${ZLIB_INCLUDE_DIRS} )
    target_link_libraries( embedded_mysql ${ZLIB_LIBRARIES} )
endif( ZLIB_FOUND )

execute_process(COMMAND mysql_config --include
        OUTPUT_VARIABLE MYSQL_INCLUDE)
execute_process(COMMAND mysql_config --libmysqld-libs
        OUTPUT_VARIABLE MYSQL_LIBS)

string(STRIP ${MYSQL_LIBS} MYSQL_LIBS)

target_compile_options(embedded_mysql PUBLIC ${MYSQL_INCLUDE})
target_link_libraries(embedded_mysql ${MYSQL_LIBS})

You can see the code in github here