Sqlite C接口获得单值结果

Question

当我输入Sqlite

SELECT Count(*) FROM tabl;

它返回一个数字.

在准备语句后如何使用C接口获取此数字？

Answer 1

打开数据库文件,准备语句,制作步骤(即,如果结果中有多行,则必须逐个获取它们),提取列值,最终确定语句,关闭数据库.

像这样的东西:

sqlite3_stmt* stmt = NULL;

sqlite3* local_db = NULL;

sqlite3_open("filename.sqlite", &local_db);

int retval, idx;
char sql[2048];

sprintf(sql, "select Something from Somewhere;");

// execute statement
retval = sqlite3_prepare_v2(local_db, sql, -1, &stmt, 0);

if(retval)
{
    printf("Selecting data from DB Failed (err_code=%d)\n", retval);
    return;
}

// iterate rows
idx = 0;

// for multiple results
while(1)
{
    // fetch a row's status
    retval = sqlite3_step(stmt);

    if(retval == SQLITE_ROW)
    {
        Something =
             (int)sqlite3_column_int(stmt, 0);
             // or other type - sqlite3_column_text etc.
        // ... fetch other columns, if there are any
    }
    else if(retval == SQLITE_DONE)
    {
        break;
    }
    else
    {
        sqlite3_finalize(stmt);
        printf("Some error encountered\n");
        break;
    }
}

sqlite3_finalize(stmt);

sqlite3_close(local_db);

使用此代码,查找所有API调用(open,prepare_v2,step,column,finalize).

如果这很难,那么首先你应该熟悉C本身.