使用外部库进行编译

我在从 github 项目编译基于 C++ 的 jwt 库的示例(示例代码)之一时遇到问题：jwt-cpp 我克隆了它并使用自述文件中提供的步骤对其进行了编译，这似乎很成功。

之后我做了一个ldconfig.

现在，我正在尝试构建示例代码。

#include <iostream>
#include "jwt/jwt_all.h"
using json = nlohmann::json;
int main()
{
// Setup a signer
HS256Validator signer("secret!");
// Create the json payload that expires 01/01/2017 @ 12:00am (UTC)
json payload = {{"sub", "subject"}, {"exp", 1483228800}};
// Let's encode the token to a string
auto token = JWT::Encode(signer, payload);
std::cout << token << std::endl;
}

我使用终端上的命令编译它，上面写着：

g++ -std=c++11 
-I/usr/local/include 
-I/usr/local/include 
/usr/local/lib/libjwt.a 
/usr/local/lib/libcrypto.a 
sign.cpp -o sign

它会导致以下错误：

/tmp/ccX4ghoR.o: In function `main':
sign.cpp:(.text+0x24e): undefined reference to 
JWT::Encode(MessageSigner const&, nlohmann::basic_json<std::map, 
std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> >, bool, long, unsigned long, double, 
std::allocator, nlohmann::adl_serializer> const&, 
nlohmann::basic_json<std::map, std::vector, 
std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> >, bool, long, unsigned long, double, 
std::allocator, nlohmann::adl_serializer>)'
/tmp/ccX4ghoR.o: In function 
`HS256Validator::HS256Validator(std::__cxx11::basic_string<char, 
std::char_traits<char>, std::allocator<char> > const&)': sign.cpp:(.text._ZN14HS256ValidatorC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN14HS256ValidatorC5ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x21): undefined reference to `EVP_sha256' sign.cpp:(.text._ZN14HS256ValidatorC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN14HS256ValidatorC5ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x5f): undefined reference to `HMACValidator::HMACValidator(std::__cxx11::basic_string<char, 
std::char_traits<char>, std::allocator<char> > const&, evp_md_st 
const*, std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> > const&)'
/tmp/ccX4ghoR.o:
(.rodata._ZTV14HS256Validator[_ZTV14HS256Validator]+0x20): undefined 
reference to `HMACValidator::Verify(nlohmann::basic_json<std::map, 
std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> >, bool, long, unsigned long, double, 
std::allocator, nlohmann::adl_serializer> const&, unsigned char 
const*, unsigned long, unsigned char const*, unsigned long) const'
/tmp/ccX4ghoR.o:
(.rodata._ZTV14HS256Validator[_ZTV14HS256Validator]+0x28): undefined 
reference to `HMACValidator::toJson[abi:cxx11]() const'
/tmp/ccX4ghoR.o:
(.rodata._ZTV14HS256Validator[_ZTV14HS256Validator]+0x38): undefined 
reference to `MessageValidator::Accepts(nlohmann::basic_json<std::map, 
std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, 
std::allocator<char> >, bool, long, unsigned long, double, 
std::allocator, nlohmann::adl_serializer> const&) const'
/tmp/ccX4ghoR.o:
(.rodata._ZTV14HS256Validator[_ZTV14HS256Validator]+0x40): undefined 
reference to `HMACValidator::Sign(unsigned char const*, unsigned long, 
unsigned char*, unsigned long*) const'
/tmp/ccX4ghoR.o: In function `HS256Validator::~HS256Validator()':
sign.cpp:
(.text._ZN14HS256ValidatorD2Ev[_ZN14HS256ValidatorD5Ev]+0x20): 
undefined reference to `HMACValidator::~HMACValidator()'
/tmp/ccX4ghoR.o:
(.rodata._ZTI14HS256Validator[_ZTI14HS256Validator]+0x10): undefined 
reference to `typeinfo for HMACValidator'
collect2: error: ld returned 1 exit status

我试过什么：

我已经通读了这些问题，以了解我可能做错了什么： 如何使用库并使用linux终端的外部库编译C文件，尽管第二个问题专门针对C而不是C++，但那里的问题和解决方案也适用于C++。

我还尝试了命令行编译的变体，例如，

g++ -std=c++11 
-I/usr/local/include 
-I/usr/local/include 
-L/usr/local/lib/ 
-lcrypto -ljwt 
sign.cpp -o sign

我熟悉这样一个事实，即当我做一个-lfoo时，链接器试图在-L选项提供的位置找到一个libfoo.a。

我已经确认用于编译的选项包含它们应该包含的内容。
对于-I选项：我可以在/usr/local/include
中看到jwt和openssl目录对于-L选项：我可以看到libjwt.a，libssl.a，libcrypto.a，libssl.so等/usr/local/lib/

问题： 我在编译此示例时做错了什么？