如何从MATLAB中输入的字符串创建函数指针? [英] How can I create function pointers from a string input in MATLAB?

问题描述

如果我在MATLAB中使用inline函数，则可以创建一个函数名称，该名称可能会根据之前的选择而有所不同:

If I use the inline function in MATLAB I can create a single function name that could respond differently depending on previous choices:

if (someCondition)
  p = inline('a - b','a','b');
else
  p = inline('a + b','a','b');
end

c = p(1,2);
d = p(3,4);

但是我正在创建的内联函数变得非常具有史诗性，因此我想将它们更改为其他类型的函数(即m文件，子函数或嵌套函数).

But the inline functions I'm creating are becoming quite epic, so I'd like to change them to other types of functions (i.e. m-files, subfunctions, or nested functions).

假设我有m个文件，例如Mercator.m，KavrayskiyVII.m等(都带有phi和lambda的值)，我想将所选函数分配给p以与上面相同的方式进行调用，因此我可以多次调用它(使用可变大小的矩阵以及使用eval可能导致的混乱或完全混乱的事情).

Let's say I have m-files like Mercator.m, KavrayskiyVII.m, etc. (all taking a value for phi and lambda), and I'd like to assign the chosen function to p in the same way as I have above so that I can call it many times (with variable sized matrices and things that make using eval either impossible or a total mess).

我有一个变量type，它将是所需功能的名称之一(例如'Mercator'，'KavrayskiyVII'等).我想我需要使p成为指向type变量内部命名的函数的指针.有什么想法可以做到吗?

I have a variable, type, that will be one of the names of the functions required (e.g. 'Mercator', 'KavrayskiyVII', etc.). I figure I need to make p into a pointer to the function named inside the type variable. Any ideas how I can do this?

推荐答案

选项#1:

使用 str2func 函数(假设字符串位于type与函数的名称相同):

Option #1:

Use the str2func function (assumes the string in type is the same as the name of the function):

p = str2func(type);  % Create function handle using function name
c = p(phi, lambda);  % Invoke function handle

注意::文档中提到了以下限制:

NOTE: The documentation mentions these limitations:

使用str2func创建的函数句柄无权访问其本地工作空间之外的变量或嵌套函数.如果您的函数句柄包含这些变量或函数，则在调用句柄时MATLAB®会引发错误.

Function handles created using str2func do not have access to variables outside of their local workspace or to nested functions. If your function handle contains these variables or functions, MATLAB® throws an error when you invoke the handle.

选项2:

使用 SWITCH 语句和

选项3:

使用 EVAL 和 Andrew Janke ):

p = eval(['@' type]);  % Concatenate string name with '@' and evaluate
c = p(phi, lambda);    % Invoke function handle

正如安德鲁指出的那样，这避免了str2func的限制以及与switch语句相关的额外维护.

As Andrew points out, this avoids the limitations of str2func and the extra maintenance associated with a switch statement.

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