Wie lese ich Daten aus der SQLite-Datenbank?

Question

Ich entschied mich, SQLite zu verwenden, da es Datenbank in einer einzelnen Datei speichern kann. Ich denke, ich habe es geschafft, eine Datenbank mit SQLite Database Browser zu machen.

Wie kann ich diese Daten in einem C/C++ Programm lesen?

Answer 1

http://www.sqlite.org/quickstart.html

Answer 2

Wie über die 'An Introduction to Sqlite C/C++ Interface', und es gibt eine ganze C++ Beispiel ist here on CodeProject.

Diese Bits der mehr Voll Probe ist,

#include "CppSQLite.h" 
#include <ctime> 
#include <iostream> 
using namespace std; 
const char* gszFile = "C:\\test.db"; 

int main(int argc, char** argv) 
{ 
    try 
    { 
     int i, fld; 
     time_t tmStart, tmEnd; 
     CppSQLiteDB db; 

     cout << "SQLite Version: " << db.SQLiteVersion() << endl; 

     db.open(gszFile); 
     cout << db.execScalar("select count(*) from emp;") 
       << " rows in emp table in "; 
     db.Close(); 
    } 
    catch (CppSQLiteException& e) 
    { 
     cerr << e.errorCode() << ":" << e.errorMessage() << endl; 
    } 
} 

Answer 3

Ein Beispiel unter Verwendung von SQLite-Lese:

#include <stdio.h> 
#include <sqlite3.h> 
#include <string.h> 


int main(int argc, char** argv) 
{ 
    const char*   username = "satyam"; 
    char     q[999]; 
    sqlite3*    db; 
    sqlite3_stmt*  stmt; 
    int     row = 0; 
    int     bytes; 
    const unsigned char* text; 

    if (2 == argc) { 
     username = argv[1]; 
    } 

    q[sizeof q - 1] = '\0'; 
    snprintf(
     q, 
     sizeof q - 1, 
     "SELECT ipaddr FROM items WHERE username = '%s'", 
     username 
    ); 

    if (sqlite3_open ("test.db", &db) != SQLITE_OK) { 
     fprintf(stderr, "Error opening database.\n"); 
     return 2; 
    } 

    printf("Query: %s\n", q); 

    sqlite3_prepare(db, q, sizeof q, &stmt, NULL); 

    bool done = false; 
    while (!done) { 
     printf("In select while\n"); 
     switch (sqlite3_step (stmt)) { 
     case SQLITE_ROW: 
      bytes = sqlite3_column_bytes(stmt, 0); 
      text = sqlite3_column_text(stmt, 1); 
      printf ("count %d: %s (%d bytes)\n", row, text, bytes); 
      row++; 
      break; 

     case SQLITE_DONE: 
      done = true; 
      break; 

     default: 
      fprintf(stderr, "Failed.\n"); 
      return 1; 
     } 
    } 

    sqlite3_finalize(stmt); 

    return 0; 
} 

Answer 4

Eine Möglichkeit, es ohne weitere Wrapper zu tun

#include <stdio.h> 
#include <string> 
using std::string; 
#include <sstream> 
using std::stringstream; 

#include "sqlite3.h" 

bool find_employee(int _id) 
{ 
    bool found = false; 
    sqlite3* db; 
    sqlite3_stmt* stmt; 
    stringstream ss; 

    // create sql statement string 
    // if _id is not 0, search for id, otherwise print all IDs 
    // this can also be achieved with the default sqlite3_bind* utilities 
    if(_id) { ss << "select * from employees where id = " << _id << ";"; } 
    else { ss << "select * from employees;"; } 
    string sql(ss.str()); 

    //the resulting sql statement 
    printf("sql: %s\n", sql.c_str()); 

    //get link to database object 
    if(sqlite3_open("data/test.db", &db) != SQLITE_OK) { 
     printf("ERROR: can't open database: %s\n", sqlite3_errmsg(db)); 
     sqlite3_close(db); 
     return found; 
    } 

    // compile sql statement to binary 
    if(sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, NULL) != SQLITE_OK) { 
     printf("ERROR: while compiling sql: %s\n", sqlite3_errmsg(db)); 
     sqlite3_close(db); 
     sqlite3_finalize(stmt); 
     return found; 
    } 

    // execute sql statement, and while there are rows returned, print ID 
    int ret_code = 0; 
    while((ret_code = sqlite3_step(stmt)) == SQLITE_ROW) { 
     printf("TEST: ID = %d\n", sqlite3_column_int(stmt, 0)); 
     found = true; 
    } 
    if(ret_code != SQLITE_DONE) { 
     //this error handling could be done better, but it works 
     printf("ERROR: while performing sql: %s\n", sqlite3_errmsg(db)); 
     printf("ret_code = %d\n", ret_code); 
    } 

    printf("entry %s\n", found ? "found" : "not found"); 

    //release resources 
    sqlite3_finalize(stmt); 
    sqlite3_close(db); 

    return found; 
}