c++ - HttpQueryServiceConfiguration 总是返回 ERROR_INSUFFICIENT_BUFFER

Question

#include "stdafx.h"
#include "Http.h"
#pragma comment (lib,"Httpapi.lib")

int _tmain(int argc, _TCHAR* argv[])
{
    HTTPAPI_VERSION HttpApiVersion = HTTPAPI_VERSION_1;
    ULONG ret = NO_ERROR;
    HRESULT hr = S_OK;
    HTTPAPI_VERSION ver = HTTPAPI_VERSION_1;
    ret = HttpInitialize(ver,HTTP_INITIALIZE_SERVER|HTTP_INITIALIZE_CONFIG,NULL);
    if(ret!=NO_ERROR)
    {
        return 0;
    }

    HTTP_SERVICE_CONFIG_ID configId = HttpServiceConfigIPListenList;
    HTTP_SERVICE_CONFIG_IP_LISTEN_QUERY* query=NULL;
    ULONG size=1000;
    ULONG re = HttpQueryServiceConfiguration(NULL,configId,NULL,NULL,query,NULL,&size,NULL);
    printf("re = %d",re);
    getchar();
    return 0;
}

这个重新结果总是 122 (ERROR_INSUFFICIENT_BUFFER) 。我不知道原因。这是 HttpQueryServiceConfiguration 函数的链接: https://msdn.microsoft.com/en-us/library/windows/desktop/aa364491

Answer 1

根据您链接到的引用，您作为函数指针传递的 size 是 pReturnLength，它是一个输出 参数，并且是

A pointer to a variable that receives the number of bytes to be written in the output buffer.

[强调我的]

您提供的缓冲区大小在之前的参数中，即 OutputConfigInfoLength 参数中。当然，如果你想写入一些数据，你需要实际提供一个缓冲区来存储它，你传递 NULL 作为参数(query 被初始化为 NULL).

另请注意，如果函数因 ERROR_INSUFFICIENT_BUFFER 而失败，作为 pReturnLength 传递的变量将包含函数成功所需的实际 长度。因此，您应该做的是首先使用零缓冲区大小调用它，以获得所需的大小，然后再次调用它以实际获取信息。

有点像

HTTP_SERVICE_CONFIG_ID configId = HttpServiceConfigIPListenList;
ULONG size;
ULONG re = HttpQueryServiceConfiguration(NULL,configId,NULL,0,NULL,0,&size,NULL);

if (re != ERROR_INSUFFICIENT_BUFFER)
{
    // We got an unknown error, handle it
}
else
{
    // Allocate a buffer big enough for the data
    HTTP_SERVICE_CONFIG_IP_LISTEN_QUERY* query =
        reinterpret_cast<HTTP_SERVICE_CONFIG_IP_LISTEN_QUERY*>(new char[size]);

    // Call the function again
    re = HttpQueryServiceConfiguration(NULL,configId,NULL,0,query,size,&size,NULL);

    // Here you should have the information you want in `query`
    // Use the data

    // Free the memory
    delete[] query;
}