sqlite3 for use on IoT Linux devices

A simple example of using sqlite3 on embedded Linux, including writing, querying the first and last entries, and deleting the first and last entries. It is very convenient to read and write on IoT devices.

The two methods of using sqlite3_exec() and sqlite3_prepare() + sqlite3_step() are the same;

Note that it is best to add a sleep after creating the table to prevent errors caused by immediate writing.
 

#include "sqlite3.h"

#define MAX_LEN 1000
typedef struct rdate
{
	int type;	
    int length;
	char data[MAX_LEN];
}Rdate;
Rdate p_Rdate;
sqlite3 *db;

int ret;
int i,j;
int nrow=0;
int ncolumn = 0;
char *zErrMsg =0;
char **azResult=0; //二维数组存放结果

//nrow   
int get_db_count(sqlite3 *db) {
    char *sql = "SELECT COUNT(*) FROM Database;";
    sqlite3_stmt *stmt;
    int count = 0;
    char *zErrMsg = 0;
    int rc;

    rc = sqlite3_prepare_v2(db, sql, -1, &stmt, NULL);
    if (rc != SQLITE_OK) {
        printf("error sqlite3_prepare_v2 %d\n", rc);
        return -1;
    }
    rc = sqlite3_step(stmt);
    if (rc != SQLITE_ROW) {
        printf("error sqlite3_step: %d\n", rc);
        return -1;
    }
    count = sqlite3_column_int(stmt, 0);
    sqlite3_finalize(stmt);

    return count;
}

int get_all_db(sqlite3 *db) {
    char *sql="select *from Database";
    sqlite3_get_table(db, sql, &azResult, &nrow, &ncolumn, &zErrMsg );
    printf("nrow=%d ncolumn=%d\n", nrow, ncolumn);
    printf("the result is:\n");
    for(i = 0;i < (nrow + 1);i++){
        for(j = 0;j < ncolumn;j++){
            printf("azResult[%d]=%s\t",i * ncolumn + j,azResult[i * ncolumn + j]);
        }
        printf("\n");
    }
    sqlite3_free_table(azResult);
    return 0;
}

int get_first_db(sqlite3 *db) {
    char *sql = "SELECT * FROM Database LIMIT 1;";
    sqlite3_stmt *stmt;

    sqlite3_prepare(db, sql, strlen(sql), &stmt, 0);
    int result = sqlite3_step(stmt);
    while (result == SQLITE_ROW) {
        p_Rdate.type = sqlite3_column_int(stmt, 1);
        p_Rdate.length = sqlite3_column_int(stmt, 2);
        strcpy(p_Rdate.data, sqlite3_column_text(stmt, 3));
        printf("get_first_db: %d, %d, %s\n", p_Rdate.type, p_Rdate.length, p_Rdate.data);
        result = sqlite3_step(stmt);
    }
    sqlite3_finalize(stmt);

    return 0;
}

int get_last_db(sqlite3 *db) {
    char *sql = "SELECT * FROM Database ORDER BY ID DESC LIMIT 1;";
    sqlite3_stmt *stmt;

    sqlite3_prepare(db, sql, strlen(sql), &stmt, 0);
    int result = sqlite3_step(stmt);
    while (result == SQLITE_ROW) {
        p_Rdate.type = sqlite3_column_int(stmt, 1);
        p_Rdate.length = sqlite3_column_int(stmt, 2);
        strcpy(p_Rdate.data, sqlite3_column_text(stmt, 3));
        printf("get_last_db: %d, %d, %s\n", p_Rdate.type, p_Rdate.length, p_Rdate.data);
        result = sqlite3_step(stmt);
    }
    sqlite3_finalize(stmt);

    return 0;
}


int insert_db(sqlite3* db, Rdate *p_Rdate) {
    char sql[512] = {0};

    sqlite3_stmt *stmt;
    int feature_index;

    snprintf(sql, 512, "INSERT INTO Database (type, length, data) VALUES (%d, %d, '%s');", 
        p_Rdate->type, p_Rdate->length, p_Rdate->data);
 
    // printf("sql: %s\n", sql);

    int rc = sqlite3_prepare(db, sql, strlen(sql), &stmt, 0);
    if (rc != SQLITE_OK) {
        printf("sqlite3_prepare error: %d\n", rc);
        return -1;
    }

    sqlite3_step(stmt);
    sqlite3_finalize(stmt);

    return 0;
}

int insert_db_test(sqlite3* db){
    static int i = 0;
    p_Rdate.type = i++;
    strcpy(p_Rdate.data, "test");
    p_Rdate.length = 88;
    insert_db(db, &p_Rdate);
}

int delete_last_db(sqlite3* db){
    char *sql="delete from Database where ID = (SELECT ID FROM Database ORDER BY ID DESC LIMIT 1) ;";
    sqlite3_exec( db , sql , NULL , NULL , &zErrMsg );

#ifdef _DEBUG_
    printf("zErrMsg = %s \n", zErrMsg);
    sqlite3_free(zErrMsg);
#endif
}

int delete_first_db(sqlite3* db){
    char *sql="delete from Database where ID = (SELECT ID FROM Database LIMIT 1) ;";
    sqlite3_exec( db , sql , NULL , NULL , &zErrMsg );

#ifdef _DEBUG_
    printf("zErrMsg = %s \n", zErrMsg);
    sqlite3_free(zErrMsg);
#endif
}

int delete_all_db(sqlite3* db){
    char *sql="delete from Database;";
    sqlite3_exec( db , sql , NULL , NULL , &zErrMsg );

#ifdef _DEBUG_
    printf("zErrMsg = %s \n", zErrMsg);
    sqlite3_free(zErrMsg);
#endif
}

int open(sqlite3 *db){
    // 打开数据库 
    ret = sqlite3_open(DATABASE,&db);
    if( ret != SQLITE_OK){
        fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
        sqlite3_close(db);
        exit(1);
    }else
        printf("opened a sqlite3 database successfully!\n");
    sleep(1);
    
    //创建表
    char *sql = "CREATE TABLE IF NOT EXISTS Database("\
                "ID INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,"\
                "type INTEGER,"\
                "length INTEGER,"\
                "data TEXT);";
    int rc = sqlite3_exec(db,sql,NULL,NULL,&zErrMsg);
    if(rc != SQLITE_OK){
        fprintf(stderr, "SQL error: %s\n", zErrMsg);
        sqlite3_free(zErrMsg);
    }else{
        fprintf(stdout, "Table created successfully\n");
    }
    sleep(1);// must do before insert
}