is-empty | 易学教程

Is it possible to set an object to null?

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Further in my code, I check to see check if an object is null/empty. Is there a way to set an object to null? An object of a class cannot be set to NULL; however, you can set a pointer (which contains a memory address of an object) to NULL. Example of what you can't do which you are asking: Cat c; c = NULL;//Compiling error Example of what you can do: Cat c; //Set p to hold the memory address of the object c Cat *p = &c; //Set p to hold NULL p = NULL; While it is true that an object cannot be "empty/null" in C++, in C++17, we got std::optional to express that intent. Example use: std::optional

Replace empty cells with logical 0's before cell2mat in MATLAB

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问题 I have an array of empty cells and ones that I want to convert to a logical array, where the empty cells are zeros. When I use cell2mat, the empty cells are ignored, and I end up with a matrix of solely 1's, with no reference to the previous index they held. Is there a way to perform this operation without using loops? Example code: for n=1:5 %generate sample cell array mycellarray{n}=1; end mycellarray{2}=[] %remove one value for testing Things I've tried: mylogicalarray=logical(cell2mat

How to check if a file is empty in Bash?

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问题 I have a file called diff.txt. Want to check if it is empty. Did something like this but couldn't get it working. if [ -s diff.txt ] then touch empty.txt rm full.txt else touch full.txt rm emtpy.txt fi 回答1: Misspellings are irritating, aren't they? Check your spelling of empty , but then also try this: #!/bin/bash -e if [ -s diff.txt ] then rm -f empty.txt touch full.txt else rm -f full.txt touch empty.txt fi I like shell scripting a lot, but one disadvantage of it is that the shell cannot

Is it possible to set an object to null?

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问题 Further in my code, I check to see check if an object is null/empty. Is there a way to set an object to null? 回答1: An object of a class cannot be set to NULL; however, you can set a pointer (which contains a memory address of an object) to NULL. Example of what you can't do which you are asking: Cat c; c = NULL;//Compiling error Example of what you can do: Cat c; //Set p to hold the memory address of the object c Cat *p = &c; //Set p to hold NULL p = NULL; 回答2: While it is true that an object

Detect if an input has text in it using CSS — on a page I am visiting and do not control?

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问题 Is there a way to detect whether or not an input has text in it via CSS? I\'ve tried using the :empty pseudo-class, and I\'ve tried using [value=\"\"] , neither of which worked. I can\'t seem to find a single solution to this. I imagine this must be possible, considering we have pseudo-classes for :checked , and :indeterminate , both of which are kind of similar thing. Please note: I\'m doing this for a \"Stylish\" style , which can\'t utilize JavaScript. Also note, that Stylish is used,

How to check empty/undefined/null string in JavaScript?

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问题 I saw this thread, but I didn\'t see a JavaScript specific example. Is there a simple string.Empty available in JavaScript, or is it just a case of checking for \"\" ? 回答1: If you just want to check whether there's any value, you can do if (strValue) { //do something } If you need to check specifically for an empty string over null, I would think checking against "" is your best bet, using the === operator (so that you know that it is, in fact, a string you're comparing against). if (strValue