[英]Passing a variable to WIN32 API LPCWSTR?
最近,我為我的軟件做了一個更新客戶端。 它使用WinHTTP連接到我公司的服務器,我想在WinHttpOpen的WINDOWS API的用戶代理部分中添加一個特殊字符串。 我需要將變量傳遞給WinHttpOpen的pwszUserAgent,它是LPCWSTR。
這是我的代碼的一部分
//convert string to wstring
wstring s2ws(const string& s)
{
int len;
int slength = (int)s.length() + 1;
len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0);
wchar_t* buf = new wchar_t[len];
MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, buf, len);
wstring r(buf);
delete[] buf;
return r;
}
//This defined string indicates a string variable I got previously
string MyVariable_grabbed_previously = "version:15.3, Date:2016/12/10"
//a flag indicate if version string variable exists
bool Version_variable = TRUE;
//define LPCWSTR for winAPI user-agent section
LPCWSTR UserAgent;
if (Version_variable) {
//version variable exist
string UA = "my custom UA & version" + MyVariable_grabbed_previously;
wstring UAWS = s2ws(UA);
UserAgent = UAWS.c_str();
}
else {
//Version variable not exist
UserAgent = L"my custom UA";
}
hSession = WinHttpOpen(UserAgent, WINHTTP_ACCESS_TYPE_NO_PROXY, WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);
但是,似乎我的程序一直使用空字符串作為User-agent,我想知道為什么我的值不能正確傳遞嗎? 我是Windows API的新手。
問題是您正在傳遞無效的指針到WinHttpOpen()
。 您正在創建一個臨時的 std::wstring
對象,獲取一個指向其數據的指針,然后在銷毀std::wstring
之后傳遞該指針。
將您的UserAgent
變量改為std::wstring
,然后在准備好傳遞它時使用c_str()
,例如:
wstring s2ws(const string& s)
{
wstring r;
int slength = s.length();
if (slength > 0)
{
int len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0);
r.resize(len);
MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, &r[0], len);
}
return r;
}
string MyVariable_grabbed_previously = "version:15.3, Date:2016/12/10";
bool Version_variable = true;
wstring UserAgent;
...
if (Version_variable) {
UserAgent = s2ws("my custom UA & " + MyVariable_grabbed_previously);
}
else {
UserAgent = L"my custom UA";
}
/* Alternatively:
UserAgent = L"my custom UA";
if (Version_variable) {
UserAgent += (L" & " + s2ws(MyVariable_grabbed_previously));
}
*/
hSession = WinHttpOpen(UserAgent.c_str(), WINHTTP_ACCESS_TYPE_NO_PROXY, WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);
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