Using scanf with NSStrings

Question

I want the user to input a string and then assign the input to an NSString. Right now my code looks like this:

NSString *word; 

scanf("%s", &word);

score 8 · Answer 1 · answered Jul 10 '10 at 22:10

8

The scanf function reads into a C string (actually an array of char), like this:

char word[40];

int nChars = scanf("%39s", word);   // read up to 39 chars (leave room for NUL)

You can convert a char array into NSString like this:

NSString* word2 = [NSString stringWithBytes:word 
                                     length:nChars
                                   encoding:NSUTF8StringEncoding];

However scanf only works with console (command line) programs. If you're trying to get input on a Mac or iOS device then scanf is not what you want to use to get user input.

answered Jul 10 '10 at 22:10

progrmr

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Does `scanf` work with `char*`? I don't want to limit the input using a fixed char array. – raffian Sep 04 '12 at 02:09
@SAFX: yes, but there are risks to using scanf, see [details here](http://stackoverflow.com/q/2430303/154803). That's why I used a fixed size buffer and limited the length in scanf. – progrmr Sep 17 '12 at 21:26
@progrmr Perhaps this is outmoded? I'm getting 'No know class method' for the stringWithBytes call. – sunny Jul 20 '15 at 22:13
I am new to Objective C and the Mac/iOS development. I writing a basic console application and wanted to use scanf with NSString and arrived at this post. I used the above method "stringWithBytes" but I got warnings that the object may not support the message. Though it was just a compile time warning, I searched more an found this "**stringWithUTF8String**". u can use it as a message as static methods of NSString or u can use it as "**initWithUTF8String**" along with alloc and get the NSString object from the character array. – Amogh Talpallikar Dec 10 '11 at 14:38
@sunny use [NSString stringWithCString:word encoding:NSASCIIStringEncoding] instead – aj_ios Jul 06 '20 at 18:46

score 7 · Answer 2 · answered Jan 23 '14 at 22:50

scanf does not work with NSString as scanf doesn’t work on objects. It works only on primitive datatypes such as:

int
float
BOOL
char

What to do?

Technically a string is made up of a sequence of individual characters. So to accept string input, you can read in the sequence of characters and convert it to a string.

use:

[NSString stringWithCString:cstring encoding:1];

Here is a working example:

NSLog(@"What is the first name?");
char cstring[40];
scanf("%s", cstring);

firstName = [NSString stringWithCString:cstring encoding:1];

Here’s an explanation of the above code, comment by comment:

You declare a variable called cstring to hold 40 characters.
You then tell scanf to expect a list of characters by using the %s format specifier.
Finally, you create an NSString object from the list of characters that were read in.

Run your project; if you enter a word and hit Enter, the program should print out the same word you typed. Just make sure the word is less than 40 characters; if you enter more, you might cause the program to crash — you are welcome to test that out yourself! :]

Taken from: RW.

It's probably better to understand if you use `NSUTF8StringEncoding` as encoding option, not the `1`. — Thomas Fankhauser, Jun 01 '14 at 14:04

Chuck · Accepted Answer · 2014-01-06T18:34:25.033

7

scanf does not work with any object types. If you have a C string and want to create an NSString from it, use -[NSString initWithBytes:length:encoding:].

edited Jan 06 '14 at 18:34

answered Jul 10 '10 at 21:08

Chuck

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How do you create a c string? Can you edit my code to show me how. – Omar Jul 10 '10 at 21:10
A C string is an array of characters so you'd simply write `char word[100]`. – W.K.S Sep 23 '12 at 10:17

W.K.S · Answer 4 · 2015-05-28T05:06:28.717

4

This is how I'd do it:

char word [40];
scanf("%s",word);

NSString * userInput = [[NSString alloc] initWithCString: word encoding: NSUTF8StringEncoding];

edited May 28 '15 at 05:06

answered Sep 23 '12 at 10:15

W.K.S

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NOTE: You don't need to put '&' Since word isn't a pointer, and is the actual character array. – ManOx Oct 30 '12 at 17:19

score 1 · Answer 5 · answered May 21 '16 at 07:13

1

Maybe this will work for you because it accepts string with spaces as well.

 NSLog(@"Enter The Name Of State");
 char name[20];
 gets(name);
 NSLog(@"%s",name);

answered May 21 '16 at 07:13

sagar

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score 1 · Answer 6 · answered Jan 13 '11 at 23:06

1

yes, but sscanf does, and may be a good solution for complex NSString parsing.

answered Jan 13 '11 at 23:06

zenchemical

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score 0 · Answer 7 · edited May 13 '16 at 13:34

0

Simple Solution is

char word[40];
scanf("%39s", word);
NSString* word2 = [NSString stringWithUTF8String:word];

edited May 13 '16 at 13:34

J Fabian Meier

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answered May 13 '16 at 12:38

singh.jitendra

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score 0 · Answer 8 · answered Oct 06 '16 at 08:24

The NSFileHandle class is an object-oriented wrapper for a file descriptor. For files, you can read, write, and seek within the file.

NSFileHandle *inputFile = [NSFileHandle fileHandleWithStandardInput];
NSData *inputData = [inputFile availableData];
NSString *word = [[NSString alloc]initWithData:inputData encoding:NSUTF8StringEncoding];

Using scanf with NSStrings

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