We have already written an initial article about DuckDB that explains initial concepts, installation and first steps. For more information, access the link:

• Meet DuckDB, a modern database

In this article, we will see how to connect to DuckDB using the API with C++

01. Download the lib and create a basic code

The DuckDB API for C++ is not yet stable, on the API page itself there is this warning:

That’s why they recommend that you use the C API which works perfectly. To do this, just access the page: https://duckdb.org/docs/installation/ and choose the data according to your system. In my case, I chose:

• Stable Release:C/C++:Linux:Direct download:x86_64

Then just click on the .zip that will be made available and download it, or download it with wget:

wget -q https://github.com/duckdb/duckdb/releases/download/v1.3.0/libduckdb-linux-amd64.zip

Unzip:

unzip libduckdb-linux-amd64.zip -d libduckdb-linux-amd64

Create a database and table, example: duckdb terminalroot.db

CREATE TABLE terminalroot (id INTEGER, name STRING);
INSERT INTO terminalroot VALUES(1, 'Marcos Oliveira');
INSERT INTO terminalroot VALUES(2, 'Mark Raasveldt');
INSERT INTO terminalroot VALUES(3, 'Hannes Muhleisen');
SELECT * FROM terminalroot;
.exit

Go into the directory you unzipped and create some basic code: cd libduckdb-linux-amd64/ && vim main.cpp

#include "duckdb.h"
#include <iostream>

int main(){
    duckdb_database db;
    duckdb_connection con;
    duckdb_result result;

    if(duckdb_open("terminalroot.db", &db) == DuckDBError){
        std::cerr << "Error opening database\n";
        return 1;
    }
    if(duckdb_connect(db, &con) == DuckDBError){
        std::cerr << "Error connecting to database\n";
        return 1; } 

    if(duckdb_query(con, "SELECT * FROM terminalroot;", &result) == DuckDBError){ 
        std::cerr << "Error executing SELECT\n"; 
        duckdb_disconnect(&con); 
        duckdb_close(&db); 
        return 1; 
    } 

    for(idx_t row = 0; row <= result.deprecated_column_count; row++){ 
        int id = duckdb_value_int32(&result, 0, row); 
        const char* name = duckdb_value_varchar(&result, 1, row); 
        std::cout << id << " | " << name << '\n'; 
        duckdb_free((void*)name); // free varchar memory 
    } 

    duckdb_destroy_result(&result); 
    duckdb_disconnect(&con);
    duckdb_close(&db);
}

Compile and run:

g++ main.cpp libduckdb.so
LD_LIBRARY_PATH=. ./a.out

Probable output:

1 | Marcos Oliveira
2 | Mark Raasveldt
3 | Hannes Muhleisen

Install on the system

If you want to install on your system and compile with the -lduckdb flag, run the commands below:

• 01. Move .h to include:

sudo mkdir -p /usr/local/include/duckdb
sudo cp duckdb.h /usr/local/include/duckdb/

• 02. Move the dynamic library to lib

  And update the system’s shared library cache.

sudo cp libduckdb.so /usr/local/lib/
sudo ldconfig

After that, just test with the flag and you don’t even need to be in the folder with the downloaded files or use the LD_LIBRARY_PATH environment variable:

But you need terminalroot.db, if you put the absolute path, e.g.: "/home/$USER/.db/terminalroot.db" your binary will run regardless of where you are in the system!

g++ main.cpp -lduckdb
./a.out

If you want to create .pc for pkg-config, expand the procedure below:

prefix=/usr/local
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: DuckDB
Description: DuckDB embedded database
Version: 1.2.1
Libs: -L${libdir} -lduckdb
Cflags: -I${includedir}/duckdb

sudo mkdir -p /usr/local/lib/pkgconfig
sudo vim /usr/local/lib/pkgconfig/duckdb.pc
# paste the above content

export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$PKG_CONFIG_PATH

I tried the static library libduckdb_static.a, but had problems, but if you prefer, try:

g++ main.cpp libduckdb_static.a -I. -ldl -pthread -lm -lz -static-libstdc++ -static-libgcc

If you also have problems, check for missing dependencies:

nm libduckdb_static.a | grep " U "

("U" = undefined symbol)

Or use ldd ./a.out to see if there are still dynamic libs hanging.

In my case none of these steps worked, but see if they apply to you too.

Useful links

• For .hpp: https://stackoverflow.com/questions/71782764/how-to-add-duckdb-library-in-c-program
• https://duckdb.org/docs/stable/clients/cpp
• https://duckdb.org/docs/stable/clients/c/connect

duckdb sql cpp

Marcos Oliveira

Software developer

https://github.com/terroo