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準(zhǔn)備用Win32 API和ODBC來(lái)訪問(wèn)數(shù)據(jù)庫(kù)；

代碼如下；

/*------------------------------------------------------------win32, ODBC, by bobo, 2018-09-09------------------------------------------------------------*/#include <windows.h> #include "sql.h" #include "sqlext.h" #include "sqltypes.h" #include "sqlucode.h" #include "odbcss.h"LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM); #define DSNAME "testDS1" #define DSUSERNAME "sa" #define DSUSERPWD "123"#pragma comment(lib, "odbc32.lib")SQLRETURN ret; SQLHENV henv; SQLHDBC hdbc;int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,PSTR szCmdLine, int iCmdShow) {static TCHAR szAppName[] = TEXT ("HelloWin") ;HWND hwnd ;MSG msg ;WNDCLASS wndclass ;wndclass.style = CS_HREDRAW | CS_VREDRAW ;wndclass.lpfnWndProc = WndProc ;wndclass.cbClsExtra = 0 ;wndclass.cbWndExtra = 0 ;wndclass.hInstance = hInstance ;wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ;wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;wndclass.lpszMenuName = NULL ;wndclass.lpszClassName = szAppName ;if (!RegisterClass (&wndclass)){MessageBox (NULL, TEXT ("This program requires Windows NT!"), szAppName, MB_ICONERROR) ;return 0 ;}hwnd = CreateWindow (szAppName, // window class nameTEXT ("The Hello ODBC"), // window captionWS_OVERLAPPEDWINDOW, // window styleCW_USEDEFAULT, // initial x positionCW_USEDEFAULT, // initial y position300, // initial x size100, // initial y sizeNULL, // parent window handleNULL, // window menu handlehInstance, // program instance handleNULL) ; // creation parametersShowWindow (hwnd, iCmdShow) ;UpdateWindow (hwnd) ;while (GetMessage (&msg, NULL, 0, 0)){TranslateMessage (&msg) ;DispatchMessage (&msg) ;}return msg.wParam ; }LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {HDC hdc ;PAINTSTRUCT ps ;RECT rect ;DWORD err;switch (message){case WM_CREATE:ret= SQLAllocEnv(&henv); ret = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);//ret = SQLConnect(hdbc, (unsigned char *)"testDS1", SQL_NTS, (unsigned char *)"sa", SQL_NTS,(unsigned char *)"123", SQL_NTS);ret = SQLConnect(hdbc, (SQLCHAR*)"testDS41", SQL_NTS, (SQLCHAR*)"sa", SQL_NTS,(SQLCHAR*)"123", SQL_NTS);//err=GetLastError();if (ret == SQL_SUCCESS || ret == SQL_SUCCESS_WITH_INFO) //成功連接到數(shù)據(jù)庫(kù){MessageBox (NULL, TEXT ("SUCCESS"), TEXT ("HelloODBC"), 0);}else{MessageBox (NULL, TEXT ("FAIL"), TEXT ("HelloODBC"), 0);}return 0 ;case WM_PAINT:hdc = BeginPaint (hwnd, &ps) ;GetClientRect (hwnd, &rect) ;DrawText (hdc, TEXT ("Hello, ODBC!"), -1, &rect,DT_SINGLELINE | DT_CENTER | DT_VCENTER) ;EndPaint (hwnd, &ps) ;return 0 ;case WM_DESTROY:PostQuitMessage (0) ;return 0 ;}return DefWindowProc (hwnd, message, wParam, lParam) ; }

在調(diào)試的時(shí)候發(fā)現(xiàn)SQLConnect總是返回1，不知道是否連接成功；
使用ODBC的預(yù)定義值來(lái)判斷是否連接成功；
原來(lái)，
SQL_SUCCESS的enum值為0， SQL_SUCCESS_WITH_INFO的enum值為1；

進(jìn)入調(diào)試，查看一下；
henv和hdbc兩個(gè)句柄已經(jīng)分配成功；ret為1；

這兩種寫法一樣；
ret = SQLConnect(hdbc, (unsigned char *)"testDS1", SQL_NTS, (unsigned char *)"sa", SQL_NTS,(unsigned char *)"123", SQL_NTS);
ret = SQLConnect(hdbc, (SQLCHAR*)"testDS41", SQL_NTS, (SQLCHAR*)"sa", SQL_NTS,(SQLCHAR*)"123", SQL_NTS);
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SQL_NTS參數(shù)的位置，本來(lái)是字符串的長(zhǎng)度，此處可以用預(yù)定義的SQL_NTS代替；
NTS => "Null-Terminated String"

如果參數(shù)對(duì)就連接成功，改個(gè)不對(duì)的參數(shù)，例如"testDS101"，則會(huì)失敗；

如果構(gòu)建時(shí)報(bào)錯(cuò)
cannot open Debug/XXXX.exe for writing
關(guān)閉開(kāi)發(fā)環(huán)境，重來(lái)；或者看任務(wù)管理器里，正在做的程序是否還在運(yùn)行，結(jié)束之即可；

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另外需要先在系統(tǒng)中建立ODBC數(shù)據(jù)源；

先做這么多吧，這活老難了；

截圖如下；

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