小编Don*_*uck的帖子

我已经使用了以下C++经验法则很长时间了:

如果类覆盖其基类中的函数,则应在基类中声明该函数virtual.

我想我从这个规则中遇到了一个例外.为了判断这是否合理,或者指出我的设计存在缺陷,我问的是这个问题.我想得到例子或更好的规则.

编辑:我试着在这里描述我的用例,我明白我并不需要继承!

我想问一个普遍的问题.谢谢你的回答!

我可以在paypal IPN中提供我的localhost网址来发回消息以通知并处理它吗？

要么...

我是否需要实时服务器URL来处理(我猜这是对的)因为paypal在发送消息时知道实时URL,但它从不知道localhost url发送消息.

任何人都可以告诉我,我需要实时服务器URL或我可以使用localhost因为我不确定.

如果我需要实时URL,我如何在visual studio中调试和开发我的功能(发送邮件等)？

有没有人有一个小例子或一些有用的链接？

我正在使用gedit并且我有一个非常庞大的线,我无法看到完整的线,因为gedit卡住了.
所以,我想在gedit中做自动换行.
我搜索了但是我没有在gedit中找到自动换行选项.

我怎么能用gedit包装？

让我们说我们上课了

class A
{
    int x;
public:
    void sayHi()
    {
        cout<<"Hi";
    }
};

int main()
{
    A *a=NULL;
    a->sayHi();
}

上面的代码将在Turbo C(我测试过的地方)上编译并Hi作为输出打印.

我原以为a是因为崩溃了NULL.sayHi()它说,如果我将功能虚拟化,那就更多了

Abnormal temination(Segmentation fault in gcc) 

我知道很多都是依赖于实现的,但是如果有人可以对任何实现有所启发,或者只是给出一个概述它会非常好.

我使用此方法导航到url,触发事件而不是将url推送到浏览器历史记录.但是Backbone.history.navigate(url,{trigger:true, replace: true})从历史中替换以前的URL.示例:浏览器hystory

之前

localhost:port/url

Backbone.history.navigate(url + '/list',{ trigger:true, replace: true })

预期:路由触发事件url + '/list'和浏览器历史记录localhost:port/url 实际上:触发事件但浏览器历史记录localhost:port/#url/list.以前的网址被替换

我想在python中使用sklearn.qda包.我已成功安装它,但是当Itry导入它时,我收到以下错误消息.任何人都可以告诉我该怎么做才能解决这个问题？

In [3]: from sklearn.qda import QDA
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-3-7d7abf937d66> in <module>()
----> 1 from sklearn.qda import QDA

/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sklearn/qda.py in <module>()
     12 
     13 from .base import BaseEstimator, ClassifierMixin
---> 14 from .utils.fixes import unique
     15 from .utils import check_arrays, array2d
     16 

/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sklearn/utils/__init__.py in <module>()
      7 import warnings
      8 
----> 9 from .murmurhash import murmurhash3_32
     10 from .validation import (as_float_array, check_arrays, safe_asarray,
     11                          assert_all_finite, array2d, atleast2d_or_csc,

ImportError: cannot import name murmurhash3_32

我在django应用程序中使用matplotlib,并希望直接返回渲染的图像.到目前为止,我可以去plt.savefig(...),然后返回图像的位置.

我想做的是:

return HttpResponse(plt.renderfig(...), mimetype="image/png")

有任何想法吗？

我在laravel 5.1中配置了dingo包,但是当我尝试访问时

HTTP://本地主机:8000 /测试

它显示以下错误

{"message":"404 Not Found","status_code":404,"debug":{"line":161,"file":"C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Routing\\RouteCollection.php","class":"Symfony\\Component\\HttpKernel\\Exception\\NotFoundHttpException","trace":["#0 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Routing\\Router.php(750): Illuminate\\Routing\\RouteCollection->match(Object(Dingo\\Api\\Http\\Request))","#1 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Routing\\Router.php(659): Illuminate\\Routing\\Router->findRoute(Object(Dingo\\Api\\Http\\Request))","#2 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Routing\\Router.php(635): Illuminate\\Routing\\Router->dispatchToRoute(Object(Dingo\\Api\\Http\\Request))","#3 C:\\wamp64\\www\\second\\vendor\\dingo\\api\\src\\Routing\\Adapter\\Laravel.php(81): Illuminate\\Routing\\Router->dispatch(Object(Dingo\\Api\\Http\\Request))","#4 C:\\wamp64\\www\\second\\vendor\\dingo\\api\\src\\Routing\\Router.php(513): Dingo\\Api\\Routing\\Adapter\\Laravel->dispatch(Object(Dingo\\Api\\Http\\Request), 'v1')","#5 C:\\wamp64\\www\\second\\vendor\\dingo\\api\\src\\Http\\Middleware\\Request.php(126): Dingo\\Api\\Routing\\Router->dispatch(Object(Dingo\\Api\\Http\\Request))","#6 [internal function]: Dingo\\Api\\Http\\Middleware\\Request->Dingo\\Api\\Http\\Middleware\\{closure}(Object(Dingo\\Api\\Http\\Request))","#7 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(139): call_user_func(Object(Closure), Object(Dingo\\Api\\Http\\Request))","#8 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Foundation\\Http\\Middleware\\VerifyCsrfToken.php(50): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#9 [internal function]: Illuminate\\Foundation\\Http\\Middleware\\VerifyCsrfToken->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#10 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, Array)","#11 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\View\\Middleware\\ShareErrorsFromSession.php(49): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#12 [internal function]: Illuminate\\View\\Middleware\\ShareErrorsFromSession->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#13 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, Array)","#14 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Session\\Middleware\\StartSession.php(62): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#15 [internal function]: Illuminate\\Session\\Middleware\\StartSession->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#16 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, Array)","#17 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Cookie\\Middleware\\AddQueuedCookiesToResponse.php(37): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#18 [internal function]: Illuminate\\Cookie\\Middleware\\AddQueuedCookiesToResponse->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#19 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, Array)","#20 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Cookie\\Middleware\\EncryptCookies.php(59): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#21 [internal function]: Illuminate\\Cookie\\Middleware\\EncryptCookies->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#22 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, Array)","#23 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Foundation\\Http\\Middleware\\CheckForMaintenanceMode.php(44): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Dingo\\Api\\Http\\Request))","#24 [internal function]: Illuminate\\Foundation\\Http\\Middleware\\CheckForMaintenanceMode->handle(Object(Dingo\\Api\\Http\\Request), Object(Closure))","#25 C:\\wamp64\\www\\second\\vendor\\laravel\\framework\\src\\Illuminate\\Pipeline\\Pipeline.php(124): call_user_func_array(Array, …

我想在HTML5中测量canvas和svg之间的性能.

到目前为止我已经完成了.我在svg和canvas中创建了多个圆圈.两者都具有500 x 500的元件宽度和高度.

我发现我正在衡量脚本编写时间.如果我在Chrome中使用开发工具,则脚本编写时间几乎等于我测量的时间.现在,我该如何测量渲染时间？将是一个带有单独的canvas和svg circle创建和devtools的代码,用于渲染比较svg和canvas渲染性能的好方法吗？

<html>
    <head>
        <script type="text/javascript">
            var svgNS = "http://www.w3.org/2000/svg";
            function createCircle1() {
                var t3 = performance.now();
                for (var x = 1; x <= 1000; x++) {
                    for (var y = 1; y <= 100; y++) {
                        var c = document.getElementById("myCanvas");
                        var ctx = c.getContext("2d");
                        ctx.beginPath();
                        ctx.arc(x, y, 5, 0, 2 * Math.PI);
                        ctx.stroke();

                    }
                }
                var t4 = performance.now();

                console.log("canvas time " + (t4 - t3) + " milliseconds.")

                var t0 = performance.now();
                for (var …

我有一个关于动态内存分配的问题.

上下文:我正在编写一个程序来读取单词的文本文件,并计算每个单词出现的频率(每行一个单词).

这个特殊的函数读取文件,计算行和字符,然后动态地将内存分配给字符串指针数组,一个数组存储每行的字符数和字符串本身.(其他部分与我的问题不太直接相关).

问题:如果空间不足,我应该多久重新分配一次内存？我设置了一个常量("memstart")来设置初始内存分配值.在下面的代码片段中,我重新分配了"memstart"值的每一行.如果重新分配更大的内存块而不是每次增加1"变量类型"的内存空间,程序是否会更快？

对于这样的事情,最佳做法是什么？

代码剪辑:

int read_alloc(FILE* fin, FILE *tmp, char **wdp, int *sz){
    int line_cnt= 0, chr, let=1;
    do{
        chr=getc(fin);
        let++;          
        //count characters

        if(chr!=EOF){
            chr=tolower(chr);
            fputc(chr, tmp);
        }               
        //convert to lcase and write to temp file

        if ('\n' == chr || chr==EOF){
            sz[(line_cnt)]=((let)*sizeof(char));            //save size needed to store string in array
            *(wdp+(line_cnt))=malloc((let)*sizeof(char));   //allocate space for the string
            if ((line_cnt-1) >= memstart){
                realloc(wdp, (sizeof(wdp)*(memstart+line_cnt)));    //if more space needed increase size
                realloc(sz, (sizeof(sz)*(memstart+line_cnt)));
            }
            line_cnt++;         
            let=1;
        }
    } …