我试图理解以下代码,但我被困在
[=](ostream outFile){}
这个参数只是声明一个新的空变量/类?或者正在获得任何以前的 ostream 价值?
如果可能,请尽可能多地解释,因为我是 lambdas 新手
#include "stdafx.h"
#include <cpprest/http_client.h>
#include <cpprest/filestream.h>
using namespace utility; // Common utilities like string conversions
using namespace web; // Common features like URIs.
using namespace web::http; // Common HTTP functionality
using namespace web::http::client; // HTTP client features
using namespace concurrency::streams; // Asynchronous streams
int main(int argc, char* argv[])
auto fileStream = std::make_shared<ostream>();
// Open stream to output file.
pplx::task<void> requestTask = fstream::open_ostream(U("results.txt"))
.then([=](ostream outFile){
*fileStream = outFile;
// Create http_client to send the request.
http_client client(U("https://localbitcoins.com"));
// Build request URI and start the request.
uri_builder builder(U("/api/payment_methods/"));
//builder.append_query(U("q"), U("cpprestsdk github"));
return client.request(methods::GET, builder.to_string());
})
// Handle response headers arriving.
.then([=](http_response response){
printf("Received response status code:%u\n", response.status_code());
// Write response body into the file.
return response.body().read_to_end(fileStream->streambuf());
})
// Close the file stream.
.then([=](size_t){
return fileStream->close();
});
// Wait for all the outstanding I/O to complete and handle any exceptions
try
{
requestTask.wait();
}
catch (const std::exception &e)
{
printf("Error exception:%s\n", e.what());
}
return 0;
}