exist,matlab中的exist是什么意思

exist用来判断变量或函数是否存在： exist Check if variables or functions are defined. exist('A') returns: 0 if A does not exist 1 if A is a variable in the workspace 2 if A is an M-file on MATLAB's search path. It also returns 2 when A is the full pathname to a file or when A is the name of an ordinary file on MATLAB's search path 3 if A is a MEX-file on MATLAB's search path 4 if A is a Simulink model or library file on MATLAB's search path 5 if A is a built-in MATLAB function 6 if A is a P-file on MATLAB's search path 7 if A is a directory 8 if A is a class (exist returns 0 for Java classes if you start MATLAB with the -nojvm option.) exist('A') or exist('A.EXT') returns 2 if a file named 'A' or 'A.EXT' and the extension isn't a P or MEX function extension. exist('A','var') checks only for variables. exist('A','builtin') checks only for built-in functions. exist('A','file') checks for files or directories. exist('A','dir') checks only for directories. exist('A','class') checks only for classes. If A specifies a filename, MATLAB attempts to locate the file, examines the filename extension, and determines the value to return based on the extension alone. MATLAB does not examine the contents or internal structure of the file. When searching for a directory, MATLAB finds directories that are part of MATLAB's search path. They can be specified by a partial path. It also finds the current working directory specified by a partial path, and subdirectories of the current working directory specified by a relative path. exist returns 0 if the specified instance isn't found.

不及物动词vi. coinhere [,kəuin'hiə] 包括在同一事物内 形容词adj：. included [ɪn'kluːdɪd] 包括的 形容词adj：inclusive [ɪn'kluːsɪv] 包括的，包含的 知识延展: 词组： inclusive of 把…包括在内 all inclusive 无所不包的；包括一切的；总括 included in 被包括；被包容 included angle 坡口角度 curriculum included 课程包括 双语造句： The freight is included in the account. 运费包括在账内。 You can call external programs, and put that call in the menus, but for $500 one expects everybell and whistle to be included. 您可以调用外部程序，然后将该调用放在菜单中，但既然支付了$500，人们希望它包括每个提醒和警告。 This process should be inclusive of all departments and all situations. 此过程应该包括所有部门和所有的情况。 As a convenience, I use the term "mechanism," as in the phrase "governance mechanism" to beall-inclusive of the components identified above. 为了方便起见，如在短语“治理机制”中一样，我使用术语“机制”来包括上面所识别的所有组成部分。

一、表达意思不同 1、persevere：vi. 坚持；不屈不挠；固执己见（在辩论中） 2、persist：存留，坚持；持续，固执，坚持说，反复说 3、insist：vt. 坚持，强调，坚持，强调 二、含义侧重不同 1、persevere：含褒义，强调坚持不懈的努力。 2、persist：用于褒义指坚持继续做某事，但更常用于贬义，指不听劝告，顽固坚持。 3、insist：通常用于对意见、主张等地坚持。 扩展资料： “persevere”的近义词：stay 1、读音：英 [steɪ] 、美 [steɪ] 2、表达意思：vi. 停留；坚持；暂住；停下； 坚持；暂住；抑制、n. 逗留；停止；支柱 3、相关短语： stay away 不在家 ; 外出 ; 离开 ; 远离 stay by 守在一边 ; 详细翻译 heel stay 贴脚条 ; 裤中线 ; 揭脚条 eyelet stay 鞋眼片 ; 鞋眼 ; 鞋带 stay idle 投闲置散 ; 保持空闲 stay angry 生气 ; 持续生气 ; 一直在生气 4、例句：Gordon stayed at The Park Hotel, Milan. 戈登住在了米兰的帕克酒店。

exist name
等价于 r=exist(name) ,在程序里面这样更加实用
0 不存在则返回值
1 name 可以是变量名，如果存在，返回值
2 函数名、m 文件名，存在则返回值
3 mex 文件、dll 文件，存在则返回值
4 内嵌的函数，存在则返回值
5 p码文件 ， 存在则返回值
6 目录，存在则返回值
7 路径，存在则返回值
8 Java class，存在则返回值

A = exist('name','kind')
name 可以是变量名，函数名、m 文件名、mex 文件、dll 文件、内嵌的函数、p码文件、目录、路径、Java class

kind可以是 ：
builtin 内嵌函数
class Java class
dir 目录
file 文件或者目录
var 变量

应用举例
type = exist('plot') %说明当前目录下存在plot这个内嵌函数
type =
5

X=rand(1,1)
X =
0.9593

matabc



r=exist('X')
r =
1

r=exist('X','var')
r =
1
matabc


还有一个非常有用的，曾经在论坛讨论过
如何判定一个结构体为空
s = struct
s =
1x1 struct array with no fields.

size(s) %用size不好判定
ans =
1 1

matabc


length(s) %length也一样
ans =
1

r=exist('s.field') %用exist可以判定
r =
0