If statement PostScript-比较相等值+&引用;如果;结构
我以前定义过If statement PostScript-比较相等值+&引用;如果;结构,if-statement,equality,postscript,If Statement,Equality,Postscript,我以前定义过 /smth1 [0 1 0] def /smth2 [-1 0 0] def 我需要检查它们是否相等,如果相等,执行一些操作 例如,(相等!)显示 我知道我应该使用eq,可能还有类似的东西 ... {(Equal!) show} if 但我不知道如何正确比较之前定义的smth1和smth2 请告知。您不想比较数组,而是想比较数组的内容。可以在PostScript中测试数组和其他复合对象是否相等,但这并不测试它们的内容,只测试它们是否是同一对象 例如: 如果运行它,您将看到Ar
/smth1 [0 1 0] def
/smth2 [-1 0 0] def
我需要检查它们是否相等,如果相等,执行一些操作
例如,(相等!)显示
我知道我应该使用eq
,可能还有类似的东西
... {(Equal!) show} if
但我不知道如何正确比较之前定义的smth1和smth2
请告知。您不想比较数组,而是想比较数组的内容。可以在PostScript中测试数组和其他复合对象是否相等,但这并不测试它们的内容,只测试它们是否是同一对象 例如: 如果运行它,您将看到Array1和Array2不相等,但Array1和指针相等。这是因为指针(松散地)是指向数组1的指针。事实上,PostScript的工作方式都是对同一对象的引用。而Array1和Array2是对不同对象的引用,即使它们的内容相同 因此,在本例中,您希望检索数组的每个元素,并将其与另一个数组中的相同元素进行比较。如果它们不相等,则中止,否则继续 我们将使用的有用运算符:长度、for、eq、get、dup、exch、if、ifelse 以下示例并非有效的解决方案,但应为您提供处理此问题的方法: 例1,检查长度
%!
%% First let us define two arrays of differing lengths
userdict begin %% We'll define these in user dict
/Array1 [0 0 0] def
/Array2 [0 1] def
% So when testing compound objects for equality, we should first
% start by checking the lengths (sizes) of the two objects
Array1 length % Put array1 on the stack then call the 'length' operator
% stack now contains the length of Array1
Array2 length % Put array2 on the stack then call the 'length' operator
% stack now contains the lengths of Array1 and Array2
eq % The eq operator tests the two objects on the stack to
% see if they are equal and returns a boolean
% stack now contains a boolean
% So now we declare some executable arrays, each executable array
% can be thought of as an inline function. We define one for each possible
% value; true or false
{
(Array1 and Array2 are equal!\n) print
}
{
(Array1 and Array2 are not equal!\n) print
}
% The ifelse operator consumes two executable arrays, and a boolean, from
% the operand stack. If the boolean is true it executes the first
% array, otherwise it executes the second.
ifelse
示例2,现在检查内容
%!
%% First let us define two arrays with the same contents
userdict begin %% We'll define these in user dict
/Array1 [0 0 0] def
/Array2 [0 0 0] def
Array1 length Array2 length eq
{
% The 'for' operator consumes 4 operands, the initial value of the loop counter,
% the amount to increment the counter by on each pass, and the terminating
% value of the counter, finally the executable array to execute on each pass.
% So, starting at loop count = 0, incrementing by 1 each time, and stopping
% when the counter is the length of the array. Note! Because we start at 0
% The counter is the array length - 1.
0 1 Array1 length 1 sub
{
%% Now on each pass the top element on the stack is the loop counter
%% We're going to need that twice, once for each array. So we start by
%% taking a copy and putting it on the stack
dup
%% The stack now contains: <loop count> <loop count>
%% Now get the n'th element from the first array:
get
%% The stack now contains: <loop count> <array1 element 'n'>
%% We want to use the loop counter to index the second array, but its not
%% on top of the stack, so swap the top two elements:
exch
%% Stack now contains: <array1 element 'n'> <loop count>
%% Now use the counter to get the n'th element from the second array
get
%% stack now contains: <array1 element n><array 2 element n>
%% check for equality
eq not
{
(Arrays are not equal!\n) print
} if
}
for
}{
(Arrays are not equal in length\n) print
} ifelse
%!
%%首先让我们定义两个具有相同内容的数组
userdict begin%%我们将在user dict中定义这些
/阵列1[0]def
/阵列2[0]def
阵列1长度阵列2长度等式
{
%“for”运算符使用4个操作数,即循环计数器的初始值,
%每次通过时计数器递增的量,以及终止
%计数器的值,最后是每次传递时要执行的可执行数组。
%因此,从循环计数=0开始,每次递增1,然后停止
%当计数器是数组的长度时。注意!因为我们从0开始
%计数器是数组长度-1。
0 1阵列1长度1子节点
{
%%现在,在每次传递时,堆栈上的顶部元素是循环计数器
%%我们需要两次,每个数组一次。所以我们从
%%复制并将其放在堆栈上
重复
%%堆栈现在包含:
%%现在从第一个数组中获取第n个元素:
收到
%%堆栈现在包含:
%%我们想使用循环计数器来索引第二个数组,但它不是
%%在堆栈顶部,交换顶部的两个元素:
exch
%%堆栈现在包含:
%%现在使用计数器从第二个数组中获取第n个元素
收到
%%堆栈现在包含:
%%检查是否相等
情商不
{
(数组不相等!\n)打印
}如果
}
对于
}{
(数组长度不相等\n)打印
}如果有
现在这里有一些明显的推论;数组只是容器,没有什么可以阻止数组包含另一个数组、字典或字符串
为了解决这个问题,最好定义一些函数来测试相等性,并根据需要调用它们,可能是递归的
上述函数不返回任何指示成功或失败的信息(后台通道上的输出除外)。显然,需要一个布尔结果。最简单的方法是在堆栈上粘贴一个“true”,如果相等失败,则弹出true并替换为false
函数在发现不等式时不会终止,可以使用exit操作符来完成这一操作(不过您可能需要首先实现上面的布尔值)
最后,该函数效率低下,因为它不断地从当前字典中复制相同的对象。可以重写函数来执行堆栈上的所有操作,这会更快
警告:我还没有在这里测试PostScript程序,完全可能出现打字错误:-)第33页(pdf第49页)中有一个函数示例。但这个答案也很好地解释了所有涉及的部分。
%!
%% First let us define two arrays with the same contents
userdict begin %% We'll define these in user dict
/Array1 [0 0 0] def
/Array2 [0 0 0] def
Array1 length Array2 length eq
{
% The 'for' operator consumes 4 operands, the initial value of the loop counter,
% the amount to increment the counter by on each pass, and the terminating
% value of the counter, finally the executable array to execute on each pass.
% So, starting at loop count = 0, incrementing by 1 each time, and stopping
% when the counter is the length of the array. Note! Because we start at 0
% The counter is the array length - 1.
0 1 Array1 length 1 sub
{
%% Now on each pass the top element on the stack is the loop counter
%% We're going to need that twice, once for each array. So we start by
%% taking a copy and putting it on the stack
dup
%% The stack now contains: <loop count> <loop count>
%% Now get the n'th element from the first array:
get
%% The stack now contains: <loop count> <array1 element 'n'>
%% We want to use the loop counter to index the second array, but its not
%% on top of the stack, so swap the top two elements:
exch
%% Stack now contains: <array1 element 'n'> <loop count>
%% Now use the counter to get the n'th element from the second array
get
%% stack now contains: <array1 element n><array 2 element n>
%% check for equality
eq not
{
(Arrays are not equal!\n) print
} if
}
for
}{
(Arrays are not equal in length\n) print
} ifelse