Question

我决定使用SQLite，因为它允许将数据库存储到单个文件中。我想我已经设法用SQLite Database Browser做了一个数据库。

如何在C / C ++程序中读取该数据？

Answer 1

“An Introduction to Sqlite C/C++ Interface”怎么样，并且有一个完整的C ++示例here on CodeProject。

这是更完整的样本的一部分，

#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 2

使用sqlite读取的示例：

#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 3

没有额外包装器的一种方法

#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;
}

如何从SQLite数据库中读取数据？

3 个答案: