在“测试模式"下打印信息但不在“正常执行"中 [英] Print information in "test mode" but not in "normal execution"

问题描述

我在 c++ 中使用一个应用程序，它使用一个特殊的 dprintf 函数来打印信息，这是一个例子:

I am using an application in c++ that uses a special dprintf function to print information, this is an example:

dprintf(verbose, "The value is: %d", i);

这样做是当我为测试目的定义详细信息然后打印信息时，当我在正常执行中工作时，我没有定义它并且我没有在屏幕上看到无用的信息.我的问题是我如何才能实现该功能或实现相同的想法?.

What is doing is when I define verbose for test purposes then I print the information and when I am working in normal execution I do not define it and I do not see useless information in the screen. My question is how can I do that function or implement the same idea?.

推荐答案

我尽量避免使用 var-arg c 风格的函数，主要有两个原因:

I try to avoid using var-arg c-style functions for two main reasons:

• 它们不是类型安全的，不能使用运算符<<
• 他们不知道什么时候提供的参数太少或太多

我已经创建了一种使用 boost::fusion 的方法，它以类型安全的方式提供参数.它遍历这些参数，在遇到 % 时打印出来.如果给出的参数太少或太多，则抛出异常.

I've made a way that works using boost::fusion, which is given arguments in a type-safe way. It iterates over those arguments, printing out them when a % is encountered. If too few or too many arguments were given, an exception is thrown.

仍然存在一个问题:可变参数宏在 C++ 中还不是标准.所以，我做了两个版本.一种适用于当前 C++ 的方法.您必须使用

There is one problem still: Variadic macros are not yet standard in C++. So, i have made two versions. One that work with current C++. You have to invoke it using

dprintf("name: %, value: %
", ("foo", 42));

那么.使用可变参数宏的另一个版本可以通过定义预处理器符号来使用，它使您能够编写

Then. The other version, using variadic macros, can be used by defining a preprocessor symbol, which enables you to write

dprintf("name: %, value: %
", "foo", 42);

这是代码.boost.fusion 为此提供了更多详细信息:

Here is the code. The boost.fusion provides more details for this:

#include <boost/fusion/include/sequence.hpp>
#include <boost/fusion/include/make_vector.hpp>
#include <boost/fusion/include/next.hpp>
#include <stdexcept>
#include <iostream>

template<typename IterS, typename IterSeqE>
void print_vec(IterS b, IterS e, IterSeqE, IterSeqE) {
    while(b != e) {
        if(*b == '%') {
            if(++b != e && *b == '%') {
                std::cout << '%';
            } else {
                throw std::invalid_argument("too many '%'");
            }
        } else {
            std::cout << *b;
        }
        ++b;
    }
}

template<typename IterS, typename IterSeqB, typename IterSeqE>
void print_vec(IterS b, IterS e, IterSeqB seqb, IterSeqE seqe) {
    while(b != e) {
        if(*b == '%') {
            if(++b != e && *b == '%') {
                std::cout << '%';
            } else {
                std::cout << *seqb;
                return print_vec(b, e, next(seqb), seqe);
            }
        } else {
            std::cout << *b;
        }
        ++b;
    }
    throw std::invalid_argument("too few '%'");
}

template<typename Seq>
void print_vec(std::string const& msg, Seq const& seq) {
    print_vec(msg.begin(), msg.end(), begin(seq), end(seq));
}

#ifdef USE_VARIADIC_MACRO
#  ifdef DEBUG
#    define dprintf(format, ...) 
         print_vec(format, boost::fusion::make_vector(__VA_ARGS__))
#  else 
#    define dprintf(format, ...)
#  endif
#else
#  ifdef DEBUG
#    define dprintf(format, args) 
         print_vec(format, boost::fusion::make_vector args)
#  else 
#    define dprintf(format, args)
#  endif
#endif

// test, using the compatible version. 
int main() {
    dprintf("hello %, i'm % years old
", ("litb", 22));
}

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