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Date: 一月 13, 2016

C++要点笔记(25)——默认模板类型参数

C++支持“默认模板类型参数”,即不为模板提供类型参数时,则使用这个默认的参数。举例如下:

template <typename T = ProcessBase>
struct PID 
{
    ......
}

参考资料:
what’s the purpose of typename assignment inside templates

 

在RHEL系统上使用“subscription-manager”注册和激活“subscription”

RHEL系统中注册和使用subscription是两个过程:

NOTE: With Red Hat Subscription-Manager, registration and utilization of a subscription is actually a two-part process. First register a system, then apply a subscription.

可以使用下面命令一次完成两个过程:

# subscription-manager register --username <username> --password <password> --auto-attach

在我的RHEL 7.2系统上执行上述命令:

# subscription-manager register --username=xxxx --password=xxxx --auto-attach
Registering to: subscription.rhn.redhat.com:443/subscription
The system has been registered with ID: 333486bb-xxxxxx

Installed Product Current Status:
Product Name: Red Hat Enterprise Linux Server
Status:       Subscribed

然后检查状态:

# subscription-manager list

+-------------------------------------------+
    Installed Product Status
+-------------------------------------------+
Product Name:   Red Hat Enterprise Linux Server
Product ID:     69
Version:        7.2
Arch:           x86_64
Status:         Subscribed
Status Details:
Starts:         06/29/2015
Ends:           06/28/2016

接下来就可以使用“yum install”,“yum update”等命令安装和更新软件了,非常方便。

参考资料:
How to Register and Enable Red Hat Subscription, Repositories and Updates for RHEL 7.0 Server
How to register and subscribe a system to the Red Hat Customer Portal using Red Hat Subscription-Manager
RHEL : Register Subscription

 

Haskell笔记 (10)—— Lazy evaluation

Haskell中对表达式的计算使用的是Lazy evaluation(也称之为nonstrict evaluation):即只有表达式的值真正需要时,才会被计算。Haskell中把用来跟踪还没有计算的表达式的记录称之为trunk

 

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