The special generation sequence for those characters, listed under strings, must be used instead. Specifically this applies to the single quote character itself, which has to be written as '\''.

The difference is that basic types are copied when assigned to a variable. With pointer types, merely the pointer is copied, that way you get two variables pointing to the same thing.

For you who are accustomed to C or C++, it may seem odd that a string is a basic type as opposed to an array of char, but it is surprisingly easy to get used to.

This "something" is freed when there are no more pointers to it. Assigning a variable with a value of a pointer type will not copy this "something" instead it will only generate a new reference to it. Special care sometimes has to be taken when giving one of these types as arguments to a function; the function can in fact modify the "something". If this effect is not wanted you have to explicitly copy the value. More about this will be explained later in this chapter.

Mappings are are really just more generic arrays. However, they are slower and use more memory than arrays, so they cannot replace arrays completely. What makes mappings special is that they can be indexed on other things than integers. We can imagine that a mapping looks like this:



Each index-value pair is floating around freely inside the mapping. There is exactly one value for each index. We also have a (magical) lookup function. This lookup function can find any index in the mapping very quickly. Now, if the mapping is called m and we index it like this: m [ i ] the lookup function will quickly find the index i in the mapping and return the corresponding value. If the index is not found, zero is returned instead. If we on the other hand assign an index in the mapping the value will instead be overwritten with the new value. If the index is not found when assigning, a new index-value pair will be added to the mapping. Writing a constant mapping is easy:





([ ]) // Empty mapping

([ 1:2 ]) // Mapping with one index-value pair, the 1 is the index

([ "one":1, "two":2 ]) // Mapping which maps words to numbers

([ 1:({2.0}), "":([]), ]) // Mapping with lots of different types





As with arrays, mappings can contain any type. The main difference is that the index can be any type too. Also note that the index-value pairs in a mapping are not stored in a specific order. You can not refer to the fourteenth key-index pair, since there is no way of telling which one is the fourteenth. Because of this, you cannot use the range operator on mappings.



The following operators and functions are important:



indexing ( m [ ind ] )

As discussed above, indexing is used to retrieve, store and add values to the mapping.

addition, subtraction, union, intersection and xor

All these operators works exactly as on arrays, with the difference that they operate on the indices. In those cases when the value can come from either mapping, it will be taken from the right side of the operator. This makes it easier to add new values to a mapping with +=. Some examples:

([1:3, 3:1]) + ([2:5, 3:7]) returns ([1:3, 2:5, 3:7 ])

([1:3, 3:1]) - ([2:5, 3:7]) returns ([1:3])

([1:3, 3:1]) | ([2:5, 3:7]) returns ([1:3, 2:5, 3:7 ])

([1:3, 3:1]) & ([2:5, 3:7]) returns ([3:7])

([1:3, 3:1]) ^ ([2:5, 3:7]) returns ([1:3, 2:5])



same ( a == b )

Returns 1 if a is the same mapping as b, 0 otherwise.

not same ( a != b )

Returns 0 if a is the same mapping as b, 1 otherwise.

array indices(mapping m)

Indices returns an array containing all the indices in the mapping m.

mixed m_delete(mapping m, mixed ind)

This function removes the index-value pair with the index ind from the mapping m. It will return the value that was removed.

int mappingp(mixed m)

This function returns 1 if m is a mapping, 0 otherwise.

mapping mkmapping(array ind, array val)

This function constructs a mapping from the two arrays ind and val. Element 0 in ind and element 0 in val becomes one index-value pair. Element 1 in ind and element 1 in val becomes another index-value pair, and so on..

mapping replace(mapping m, mixed from, mixed to)

This function creates a copy of the mapping m with all values equal to from replaced by to.

mixed search(mapping m, mixed val)

This function returns the index of the 'first' index-value pair which has the value val.

int sizeof(mapping m)

Sizeof returns how many index-value pairs there are in the mapping.

array values(mapping m)

This function does the same as indices, but returns an array with all the values instead. If indices and values are called on the same mapping after each other, without any other mapping operations in between, the returned arrays will be in the same order. They can in turn be used as arguments to mkmapping to rebuild the mapping m again.

int zero_type(mixed t)

When indexing a mapping and the index is not found, zero is returned. However, problems can arise if you have also stored zeroes in the mapping. This function allows you to see the difference between the two cases. If zero_type(m [ ind ]) returns 1, it means that the value was not present in the mapping. If the value was present in the mapping, zero_type will return something else than 1.

在网站制作过程中，图片上传以及图片的大小调整是经常会用到的一个功能！

Rails结合几个plug-in可以说很智能的做到了这一点

做了一个简单的例子，系统在Windows平台上运行

1.上网下载file-column-0.3.1.tar.gz 和rmagick-win32-1.13.0_IM-6.2.9-3.zip （我当前的最新版本，到下述站点下载 http://rubyforge.org/projects/rmagick/ Linux下版本是RMagick-1.14.1.tar.gz）

2.安装rmagick，执行zip包里面的exe文件，同时把安装路径放到path环境变量里面去，否则可能会报CORE_RL_magick_.dll找不到的错误

3.安装file-column到app的vendor目录里，直接copy过去就行

引用
以下的文件配置基本上按照官方提供的sample来进行，算是用中文整合一下，谈不上原创

4.建立一个存放路径的model，在数据库中建立Entry数据库
并生成相应的scaffold：
ruby script/generate scaffold Entry upload

4.修改model，并限制只能图片上传
Java代码 复制代码

   1. class Entry < ActiveRecord::Base 
   2.   validates_format_of :image, 
   3.     :with=>/^.*(.jpg|.JPG|.gif|.GIF)$/, 
   4.     :message => "你只能上传JPG或则GIF的图片文件" 
   5.   file_column :image, :magick => {  
   6.           :versions => { "thumb" => "50x50", "medium" => "640x480>" } 
   7.         } 
   8. end 

class Entry < ActiveRecord::Base
  validates_format_of :image,
    :with=>/^.*(.jpg|.JPG|.gif|.GIF)$/,
    :message => "你只能上传JPG或则GIF的图片文件"
  file_column :image, :magick => {
          :versions => { "thumb" => "50x50", "medium" => "640x480>" }
        }
end



5.修改_form.rhtml
Java代码 复制代码

   1. <%= error_messages_for 'entry' %> 
   2.  
   3. <!--[form:entry]--> 
   4. <p><label for="entry_image">Image</label><br/> 
   5. <%= file_column_field 'entry', 'image'  %></p> 
   6. <!--[eoform:entry]--> 

<%= error_messages_for 'entry' %>

<!--[form:entry]-->
<p><label for="entry_image">Image</label><br/>
<%= file_column_field 'entry', 'image'  %></p>
<!--[eoform:entry]-->



6.修改new.rhtml
Java代码 复制代码

   1. <h1>New entry</h1> 
   2.  
   3. <%= start_form_tag 'create',:multipart => true%> 
   4.   <%= render :partial => 'form' %> 
   5.   <%= submit_tag "Create" %> 
   6. <%= end_form_tag %> 
   7.  
   8. <%= link_to 'Back', :action => 'list' %> 

<h1>New entry</h1>

<%= start_form_tag 'create',:multipart => true%>
  <%= render :partial => 'form' %>
  <%= submit_tag "Create" %>
<%= end_form_tag %>

<%= link_to 'Back', :action => 'list' %>



7.修改show.rhtml
Java代码 复制代码

   1. <% for column in Entry.content_columns %> 
   2. <p> 
   3.   <b><%= column.human_name %>:</b> <%=h @entry.send(column.name) %> 
   4.   <br> 
   5.   原始大小： 
   6.   <%= image_tag url_for_file_column 'entry', 'image' %> 
   7.   <br> 
   8.   thumb: 
   9.   <%= image_tag url_for_file_column 'entry', 'image' ,'thumb'%> 
  10.   <br> 
  11.   medium: 
  12.   <%= image_tag url_for_file_column 'entry', 'image' ,'medium'%> 
  13. </p> 
  14. <% end %> 
  15.  
  16. <%= link_to 'Edit', :action => 'edit', :id => @entry %> | 
  17. <%= link_to 'Back', :action => 'list' %> 

nil.relative_url_root的异常是由file_column_helper中的url_for_file_column方法抛出来的, 是因为在url_for_file_column方法中还使用"@request"访问Request,只要删了'@',使用Rails 2.0的request代替@request就可以了

解决办法：

vendor\plugins\file-column-0.3.1\lib下file_column.rb文件

里的

#FileUtils.mv(local_file_path, new_local_file_path) unless new_local_file_path == local_file_path
FileUtils.mv(local_file_path, new_local_file_path) unless new_local_file_path.downcase == local_file_path.downcase

class Report < ActiveRecord::Base
    acts_as_reportable
end

def index
      table = Report.report_table(:all,
      :only => %w[host_os rubygems_version user_key],
      :conditions => "user_key is not null and user_key <> ''")
      send_data table.to_csv,
      :type => "application/csv",
      :disposition => "inline",
      :filename => "report.csv"
end