c++默认参数重定义问题

简介：一般程序员都会比较懒，能赋值粘贴的就不手写（like me），但是头文件中的函数声明和源文件中的函数体定义的函数头，都有默认参数时就会报默认参数重定义的错误，一般情况下都是在头文件中定义默认参数，因为在调用函数的时候只需要看函数声明就知道参数表了。

• 代码结构如下
  cpp文件中定义函数体；

//.cpp 文件
cv::Mat adaptiveThreshold(cv::Mat grayImage, 
                            double maxval = 255,
                            int adaptiveMethod = cv::ADAPTIVE_THRESH_MEAN_C,
                            int thresholdType = cv::THRESH_BINARY_INV, 
                            int blockSize = 11,
                            double C = 15)
{
    if (grayImage.empty()) return grayImage;
    //blockSize must be an odd number,like 3,5,7...
    if (blockSize % 2 == 0) blockSize += 1;
    if (grayImage.channels() == 3) cv::cvtColor(grayImage, grayImage, cv::COLOR_BGR2GRAY);

    cv::adaptiveThreshold(grayImage, grayImage, maxval,adaptiveMethod, 
                            thresholdType, blockSize,C);
    return grayImage;
}

头文件中的函数声明如下

//.hpp文件
cv::Mat adaptiveThreshold(cv::Mat grayImage, 
                            double maxval = 255,
                            int adaptiveMethod = cv::ADAPTIVE_THRESH_MEAN_C,
                            int thresholdType = cv::THRESH_BINARY_INV, 
                            int blockSize = 11,
                            double C = 15);

• vs编译报错

imageprocess.cpp(111): error C2572: “adaptiveThreshold”: 重定义默认参数 : 参数 1
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.h(23): note: 参见“adaptiveThreshold”的声明
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.cpp(112): error C2572: “adaptiveThreshold”: 重定义默认参数 : 参数 2
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.h(23): note: 参见“adaptiveThreshold”的声明
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.cpp(113): error C2572: “adaptiveThreshold”: 重定义默认参数 : 参数 3
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.h(23): note: 参见“adaptiveThreshold”的声明
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.cpp(114): error C2572: “adaptiveThreshold”: 重定义默认参数 : 参数 4
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.h(23): note: 参见“adaptiveThreshold”的声明
1>d:\mydoc\vs-proj\calculatedistance\calculatedistance\imageprocess.cpp(115): error C2572: “adaptiveThreshold”: 重定义默认参数 : 参数 5

• 解决方法
  把.cpp文件中的函数头中的默认参数去掉就可以了,r如下：

//.cpp 文件
cv::Mat adaptiveThreshold(cv::Mat grayImage, 
                            double maxval ,
                            int adaptiveMethod ,
                            int thresholdType , 
                            int blockSize ,
                            double C )
{
    if (grayImage.empty()) return grayImage;
    //blockSize must be an odd number,like 3,5,7...
    if (blockSize % 2 == 0) blockSize += 1;
    if (grayImage.channels() == 3) cv::cvtColor(grayImage, grayImage, cv::COLOR_BGR2GRAY);

    cv::adaptiveThreshold(grayImage, grayImage, maxval,adaptiveMethod, 
                            thresholdType, blockSize,C);
    return grayImage;
}