如何将 PUT curl 映射到 CPP Curlpp？

Question

我想将下面的 curl（此 curl 在 Linux 终端中正常工作）映射/写入 cpp 代码：

curl -X PUT -u "abc" \
    "https://api123.pl" \
    -d 'symbol=EB&side=ri&quantity=3'

以下是使用 Curlpp 库的 CPP 代码：

    #include <iostream>
    #include <sstream>
    #include <curlpp/cURLpp.hpp>
    #include <curlpp/Easy.hpp>
    #include <curlpp/Options.hpp>
    using namespace curlpp::options;
    using namespace std;
    /*
    curl -X PUT -u "abc" \
        "https://api123.pl" \
        -d 'symbol=EB&side=ri&quantity=3'
    g++ name1.cpp -lcurl -lcurlpp -o name1 && ./name1
    */
    string test(const std::string &url) {
        try {
            curlpp::Cleanup cleanup;
            curlpp::Easy request;
            request.setOpt<curlpp::Options::Url>(url);
            request.setOpt(new curlpp::options::UserPwd("abc"));
            request.setOpt(new curlpp::options::CustomRequest{"PUT"});
//    /*
    //does not compile
            std::list<std::string> postContent;
            postContent.push_back("symbol:EB");
            postContent.push_back("side:ri");
            postContent.push_back("quantity:3");
            request.setOpt(new curlpp::options::PostFields(postContent));
//    */     
            std:stringstream content;
            content << request;        
            return content.str().c_str();
        }
        catch (const curlpp::RuntimeError &e) {
            std::cout << "CURLpp runtime error: " << e.what() << std::endl;
        }
        catch (const curlpp::LogicError &e) {
            std::cout << "CURLpp logic error: " << e.what() << std::endl;
        }
        throw std::string("Error");
    }
    int main(int, char **) {
        try {
            cout << test("https://api123.pl");
        }
        catch(curlpp::RuntimeError & e) {
            std::cout << e.what() << std::endl;
        }
        catch(curlpp::LogicError & e)   {
            std::cout << e.what() << std::endl;
        }
        return 0;
    }

编译时出错：

1.2putStackoverflow.cpp: In function ‘std::string getJSONAPIResultFromURL(const string&)’:
1.2putStackoverflow.cpp:31:67: error: no matching function for call to ‘curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>::OptionTrait(std::__cxx11::list<std::__cxx11::basic_string<char> >&)’
   31 |         request.setOpt(new curlpp::options::PostFields(postContent));
      |                                                                   ^
In file included from /usr/include/curlpp/Option.hpp:251,
                 from /usr/include/curlpp/Easy.hpp:31,
                 from 1.2putStackoverflow.cpp:4:
/usr/include/curlpp/Option.inl:129:1: note: candidate: ‘curlpp::OptionTrait<OptionType, opt>::OptionTrait() [with OptionType = std::__cxx11::basic_string<char>; CURLoption opt = CURLOPT_POSTFIELDS]’
  129 | OptionTrait<OptionType, option>::OptionTrait()
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/curlpp/Option.inl:129:1: note:   candidate expects 0 arguments, 1 provided
/usr/include/curlpp/Option.inl:123:1: note: candidate: ‘curlpp::OptionTrait<OptionType, opt>::OptionTrait(typename curlpp::Option<OptionType>::ParamType) [with OptionType = std::__cxx11::basic_string<char>; CURLoption opt = CURLOPT_POSTFIELDS; typename curlpp::Option<OptionType>::ParamType = const std::__cxx11::basic_string<char>&]’
  123 | OptionTrait<OptionType, option>::OptionTrait(typename Option<OptionType>::ParamType value)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/curlpp/Option.inl:123:85: note:   no known conversion for argument 1 from ‘std::__cxx11::list<std::__cxx11::basic_string<char> >’ to ‘curlpp::Option<std::__cxx11::basic_string<char> >::ParamType’ {aka ‘const std::__cxx11::basic_string<char>&’}
  123 | OptionTrait<OptionType, option>::OptionTrait(typename Option<OptionType>::ParamType value)
      |                                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
In file included from /usr/include/curlpp/Easy.hpp:31,
                 from 1.2putStackoverflow.cpp:4:
/usr/include/curlpp/Option.hpp:145:8: note: candidate: ‘curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>::OptionTrait(const curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>&)’
  145 |  class OptionTrait : public Option<OptionType>
      |        ^~~~~~~~~~~
/usr/include/curlpp/Option.hpp:145:8: note:   no known conversion for argument 1 from ‘std::__cxx11::list<std::__cxx11::basic_string<char> >’ to ‘const curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>&’
/usr/include/curlpp/Option.hpp:145:8: note: candidate: ‘curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>::OptionTrait(curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>&&)’
/usr/include/curlpp/Option.hpp:145:8: note:   no known conversion for argument 1 from ‘std::__cxx11::list<std::__cxx11::basic_string<char> >’ to ‘curlpp::OptionTrait<std::__cxx11::basic_string<char>, CURLOPT_POSTFIELDS>&&’

问题在于：

        std::list<std::string> postContent;
        postContent.push_back("symbol:EB");
        postContent.push_back("side:ri");
        postContent.push_back("quantity:3");
        request.setOpt(new curlpp::options::PostFields(postContent));

编译程序：

g++ name1.cpp -lcurl -lcurlpp -o name1 && ./name1

我不知道如何编写代码以使用 curlpp 将 curl 映射/写入 cpp。谢谢你的帮助。

Answer 1

PostFields 只是 typedef 的 cURLpp::OptionTrait<std::string, cURL::CURLOPT_POSTFIELDS>，我正在简化以下内容。

如果您仔细阅读错误消息，它们会准确地告诉您问题所在：

错误：没有匹配函数调用 'curlpp::OptionTrait<:__cxx11::basic_string>, CURLOPT_POSTFIELDS>::OptionTrait(std::__cxx11::list<:__cxx11::basic_string> >&)'

这基本上是说你不能将std::list<std::string> 传递给PostFields 的构造函数。错误详情中报告了 4 个候选构造函数，没有一个以 std::list 作为输入：

PostFields()
PostFields(const std::string&)
PostFields(const PostFields&)
PostFields(PostFields&&)

确实，如果您阅读了cURLpp documentation，则无法从std::list 创建PostFields。这是有道理的，根据cURL documentation for CURLOPT_POSTFIELDS：

传递一个 char * 作为参数，指向要在 HTTP POST 操作中发送的完整数据。您必须确保按照您希望服务器接收数据的方式格式化数据。 libcurl 不会以任何方式为您转换或编码它。例如，Web 服务器可能假定此数据是 url 编码的。

CURLOPT_POSTFIELDS 需要单个 char* 作为输入（cURLpp 使用 std::string 包装），因此您必须将 PUT 数据作为单个 url 编码字符串传递，就像在命令行上一样，例如：

request.setOpt(new curlpp::Options::PostFields("symbol=EB&side=ri&quantity=3"));

您从哪里想到可以将std::list 与PostFields 一起使用？

---

顺便说一句，根据 cURLpp 文档，在向 curlpp::Easy 对象添加选项时，您实际上并不需要使用 new：

curlpp::Easy request;
request.setOpt(curlpp::Options::Url(url));
request.setOpt(curlpp::Options::UserPwd("abc"));
request.setOpt(curlpp::Options::CustomRequest("PUT"));
request.setOpt(curlpp::Options::PostFields("symbol=EB&side=ri&quantity=3"));