无法定义DLL导入实体C ++

Question

am试图从git编译开源dll，出现以下错误：

错误（活动）无法定义dllimport实体cppkafka

错误'cppkafka :: Queue :: DEFAULT_TIMEOUT'：不允许定义dllimport静态数据成员

错误C2491'cppkafka :: KafkaHandleBase :: DEFAULT_TIMEOUT'：不允许定义dllimport静态数据成员

错误C2491'cppkafka :: BackoffPerformer :: DEFAULT_INITIAL_BACKOFF'：dllimport静态数据成员的定义不允许

错误C2491'cppkafka :: BackoffPerformer :: DEFAULT_BACKOFF_STEP'：DLLimport静态数据成员的定义不允许

错误C2491'cppkafka :: BackoffPerformer :: DEFAULT_MAXIMUM_BACKOFF'：不允许定义dllimport静态数据成员

错误C2491'cppkafka :: BackoffPerformer :: DEFAULT_MAXIMUM_RETRIES'：不允许定义dllimport静态数据成员

这些类是：

这是头文件：

//#ifdef BUILDING_MYDLL
//#define CPPKAFKA_API __declspec(dllexport)
//#else
//#define CPPKAFKA_API __declspec(dllimport)
//#endif
#ifndef CPPKAFKA_BACKOFF_PERFORMER_H
#define CPPKAFKA_BACKOFF_PERFORMER_H

#include <chrono>
#include <functional>
#include <thread>
#include "consumer.h"

namespace cppkafka {

/**
 * 
 */
class CPPKAFKA_API BackoffPerformer {
public:
    using TimeUnit = std::chrono::milliseconds;
    static const TimeUnit DEFAULT_INITIAL_BACKOFF;
    static const TimeUnit DEFAULT_BACKOFF_STEP;
    static const TimeUnit DEFAULT_MAXIMUM_BACKOFF;
    static const size_t DEFAULT_MAXIMUM_RETRIES;

    /**
     * The backoff policy to use
     */
    enum class BackoffPolicy {
        LINEAR,
        EXPONENTIAL
    };

    /**
     * Constructs an instance of backoff performer
     * 
     * By default, the linear backoff policy is used
     */
    BackoffPerformer();

    /**
     * \brief Sets the backoff policy
     *
     * \param policy The backoff policy to be used
     */
    void set_backoff_policy(BackoffPolicy policy);

    /**
     * \brief Sets the initial backoff
     *
     * The first time a commit fails, this will be the delay between the request is sent
     * and we re-try doing so 
     *
     * \param value The value to be used
     */
    void set_initial_backoff(TimeUnit value);

    /**
     * \brief Sets the backoff step
     *
     * When using the linear backoff policy, this will be the delay between sending a request
     * that fails and re-trying it
     *
     * \param value The value to be used
     */
    void set_backoff_step(TimeUnit value);

    /**
     * \brief Sets the maximum backoff
     *
     * The backoff used will never be larger than this number
     *
     * \param value The value to be used
     */
    void set_maximum_backoff(TimeUnit value);

    /**
     * \brief Sets the maximum number of retries for the commit operation
     *
     * \param value The number of retries before giving up
     *
     * \remark Setting value to 0 is equivalent to 1, i.e. it will try at least once
     */
    void set_maximum_retries(size_t value);

    /**
     * \brief Executes an action and backs off if it fails
     *
     * This will call the functor and will retry in case it returns false
     *
     * \param callback The action to be executed
     */
    template <typename Functor>
    void perform(const Functor& callback) {
        TimeUnit backoff = initial_backoff_;
        size_t retries = maximum_retries_;
        while (retries--) {
            auto start = std::chrono::steady_clock::now();
            // If the callback returns true, we're done
            if (callback()) {
                return;
            }
            auto end = std::chrono::steady_clock::now();
            auto time_elapsed = end - start;
            // If we still have time left, then sleep
            if (time_elapsed < backoff) {
                std::this_thread::sleep_for(backoff - time_elapsed);
            }
            // Increase out backoff depending on the policy being used
            backoff = increase_backoff(backoff);
        }
    }
private:
    TimeUnit increase_backoff(TimeUnit backoff);

    TimeUnit initial_backoff_;
    TimeUnit backoff_step_;
    TimeUnit maximum_backoff_;
    BackoffPolicy policy_;
    size_t maximum_retries_;
};

} // cppkafka

#endif // CPPKAFKA_BACKOFF_PERFORMER_H

.cpp：

#include <algorithm>
#include <limits>
#include "utils\backoff_performer.h"

using std::min;
using std::numeric_limits;

namespace cppkafka {

const BackoffPerformer::TimeUnit BackoffPerformer::DEFAULT_INITIAL_BACKOFF{100};
const BackoffPerformer::TimeUnit BackoffPerformer::DEFAULT_BACKOFF_STEP{50};
const BackoffPerformer::TimeUnit BackoffPerformer::DEFAULT_MAXIMUM_BACKOFF{1000};
const size_t BackoffPerformer::DEFAULT_MAXIMUM_RETRIES{numeric_limits<size_t>::max()};

BackoffPerformer::BackoffPerformer()
: initial_backoff_(DEFAULT_INITIAL_BACKOFF),
  backoff_step_(DEFAULT_BACKOFF_STEP), maximum_backoff_(DEFAULT_MAXIMUM_BACKOFF),
  policy_(BackoffPolicy::LINEAR), maximum_retries_(DEFAULT_MAXIMUM_RETRIES) {

}

void BackoffPerformer::set_backoff_policy(BackoffPolicy policy) {
    policy_ = policy;
}

void BackoffPerformer::set_initial_backoff(TimeUnit value) {
    initial_backoff_ = value;
}

void BackoffPerformer::set_backoff_step(TimeUnit value) {
    backoff_step_ = value;
}

void BackoffPerformer::set_maximum_backoff(TimeUnit value) {
    maximum_backoff_ = value;
}

void BackoffPerformer::set_maximum_retries(size_t value) {
    maximum_retries_ = value == 0 ? 1 : value;
}

BackoffPerformer::TimeUnit BackoffPerformer::increase_backoff(TimeUnit backoff) {
    if (policy_ == BackoffPolicy::LINEAR) {
        backoff = backoff + backoff_step_;
    }
    else {
        backoff = backoff * 2;
    }
    return min(backoff, maximum_backoff_);
}

} // cppkafka

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