Question

我遇到了从github项目编译基于C ++的jwt库的一个示例（示例代码）的问题：jwt-cpp 我克隆它并使用README文件中提供的步骤编译它，这似乎是成功的。

之后我做了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;
}

我用终端上的命令编译它，它说：

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

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

我尝试了什么：

我已经阅读了这些问题以了解我可能做错了什么： How to use libraries和compile C file using external library from linux terminal，虽然第二个问题专门针对C而不是C ++，但问题和解决方案也适用于C ++。

我也尝试过命令行编译的变种，例如，

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

我很熟悉当我执行-lfoo时，链接器会尝试在-L选项提供的位置找到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 适用于-I选项： 我可以在jwt中看到openssl和/usr/local/include目录 适用于-L选项： 我可以在libjwt.a

看到libssl.a，libcrypto.a，libssl.so，/usr/local/lib/等

问题：编译这个例子我做错了什么？

Answer 1

当我告诉你这个问题时，你会踢自己。

在您的程序中将源文件class Worker(QtCore.QObject): finishedParsing = QtCore.pyqtSignal(DataParser) def run(self): self._stop = False for count, file in enumerate(self._files, 1): # parse the data in the DataParser and create an object # of the files data data = DataParser(file) # emit a signal to let the window know that this data is # ready to use self.finishedParsing.emit(data) self.loaded.emit(count, file) if self._stop: break self.finished.emit() class Window(QtWidgets.QWidget): def showOpenDialog(self): if files and not self.thread.isRunning(): # do the opening stuff like written before self.worker = Worker(files) #... self.worker.finishedParsing.connect(self.addParsedData) 放在库声明之前：

sign.cpp

原因是unix链接器在命令行中没有向后看以解决依赖关系。有一些命令行开关（例如g++ -std=c++11 -I/usr/local/include -L/usr/local/lib sign.cpp -lcrypto -ljwt -o sign和--start-group）将调整此行为，但上面的内容将使您现在解除阻止。 More details here

在上面的例子中，我冒昧地删除了重复的INCLUDE路径参数。您可能甚至不需要--end-group或-I/usr/local/include部分，因为它通常已经在标准编译器路径中。

使用外部库

1 个答案: