C++ 如何从 SQLite 数据库中读取数据？
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How to read data from SQLite database?
提问by zaplec
I decided to use SQLite as it allows to store database into a single file. I think I have managed to do a database with SQLite Database Browser.
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 创建了一个数据库。
How can I read that data in a C/C++ program?
如何在 C/C++ 程序中读取该数据？
采纳答案by Preet Sangha
How about the 'An Introduction to Sqlite C/C++ Interface', and there is a whole C++ example here on CodeProject.
' Sqlite C/C++ 接口简介'怎么样，CodeProject 上有一个完整的 C++ 示例。
This is bits of the more full sample,
这是更完整样本的一部分，
#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;
}
}
回答by Satyam
A example using sqlite read:
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] = '#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;
}
';
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;
}
回答by Giles
One way to do it without additional wrappers
一种无需额外包装的方法
##代码##