As per my assignment I have to take in input from a user via a console to be used with NSString.
At the moment I have
char* name[100]; // declaring char array
NSString* firstName; // declaring the NSString
printf("Please enter first name \n");
printf("=> ");
scanf("%s", &name);
firstName = [NSString stringWithCString:name encoding:NSASCIIStringEncoding];
This works, however I am getting this warning
Incompatible pointer types sending 'char [100]' to parameter of type
'const char '
I don't want to be having these errors coming up in the code, I would like to also mention I'm using Xcode 4.2.
Can anyone explain to me why I'm getting these errors, and if I can possibly overcome them?
Many thanks in advance!
Change this:
char* name[100];
to
char name[100];
The first form creates an array of 100 pointers to char. The second one creates an array of 100 char elements. What might be confusing, is that name in that last case, is in fact a pointer, pointing to the first of these 100 char elements.
As printed with NSLog is assigned to initialize a NSString.
NSLog(#"%s", arrayChar);
NSString *str = [NSString stringWithFormat:#"%s", arrayChar];
NSLog(#"Array to String: %#",str);
Related
i got the following char array in Objective-C (Xcode):
char *incomeMessage;
NSString *str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
incomeMessage = [str UTF8String];
NSLog(#"%c", incomeMessage[0]);
NSLog(#"%c", incomeMessage[1]);
NSLog(#"%c", incomeMessage[2]);
NSLog(#"%c", incomeMessage[3]);
NSLog(#"%c", incomeMessage[4]);
NSLog(#"%c", incomeMessage[5]);
For example I get some results like this in console:
"3
2
6
1
8
4"
Now i want to replace the char in incomeMessage[2] by 4:
incomeMessage[2] = '4';
But then it gives me the error:
EXC_BAD_ACCESS
Do you have an idea, how to solve the problem?
According to the reference documentation, UTF8String returns a read-only (const char*) reference to the string data.
The reference material goes on to note:
This C string is a pointer to a structure inside the string object,
which may have a lifetime shorter than the string object and will
certainly not have a longer lifetime. Therefore, you should copy the C
string if it needs to be stored outside of the memory context in which
you use this property.
So I'd suggest following their advice and creating a copy of the array and then performing your modifications against that.
For example: http://ideone.com/mhjwZW
You might have better luck with something like:
NSString* str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
char* incomeMessage = malloc([str lengthOfBytesUsingEncoding:NSUTF8StringEncoding] + 1);
strcpy(incomeMessage, [str UTF8String]);
//now you can change things
incomeMessage[2] = '4';
//do this when you're done
free(incomeMessage);
Although, is there any particular reason why you want to use a C-string/character array as opposed to an NSMutableString? I think you might find replaceCharactersInRange:withString: a better approach generally. See also: stringByReplacingCharactersInRange:withString:.
i got the following char array in Objective-C (Xcode)
You don't, you know. All you have is a pointer. You have not set aside any actual memory; there is no array there.
incomeMessage = [str UTF8String];
All you've done in that line is repoint the pointer incomeMessage at your string's UTF8String. A string's UTF8String is immutable. Note this passage in the docs:
you should copy the C string if it needs to be stored outside of the memory context in which you use this property.
So basically, if you want to write into an array of char, your first task should be to make an array of char.
#import <Foundation/Foundation.h>
int main (int argc, char * argv[])
{
#autoreleasepool {
NSString *str = #"Programming is fun";
NSLog (#"%#", str);
}
return 0;
}
In the line
NSString *str = #"Programming is fun";
the constant string object Programming is fun is assigned to the NSString variable str. Its value is then displayed using NSLog .
The NSLog format characters %# can be used to display not just NSString objects, but other objects as well.
/*****/
The previous paragraph was from a book I read, what is really confusing to me is why is he keep using the words variable and objects interchangeably? are objects and varaibles the same thing? so far this is the only confusing part about obj-c to me.
please explain, thank you
An object is an instance of a class. Something that is allocated in memory.
A variable is a name which you use to access something like an object (NSString for example) or a primitive (int for example).
In your case so your object is an instance of NSString, that contains #"Programming is fun":
NSString *str = #"Programming is fun";
The variable to access that object is str.
I am attempting to use scanf to assign a value to an NSString, as per the answers to this question by Omar. This is the code, taken straight from progrmr's answer:
char word[40];
int nChars = scanf("%39s", word); // read up to 39 chars (leave room for NUL)
NSString* word2 = [NSString stringWithBytes:word
length:nChars
encoding:NSUTF8StringEncoding];
However, I'm getting an error on the last line that makes absolutely no sense to me:
No known class method for selector 'stringWithBytes:length:encoding:'
What in the world could be causing this error?
And yes, I do have #import <Foundation/Foundation.h> at the top of the file.
NSString does not have a stringWithBytes:length:encoding: class method, but you can use
NSString* word2 = [[NSString alloc] initWithBytes:word
length:nChars
encoding:NSUTF8StringEncoding];
Note however, that scanf() returns the number of scanned items and
not the number of scanned characters. So nChars will contain 1 and not the string length, so you should set nChars = strlen(word) instead.
A simpler alternative is (as also mentioned in one answer to the linked question)
NSString* word2 = [NSString stringWithUTF8String:word];
NSString does not respond to the selector stringWithBytes:length:encoding:. You probably wanted initWithBytes:length:encoding:.
Story in short: you might want to consider a const char C-string suitable initializer for your NSString object. Also, allocate memory before sending any initializer message to the NSString object. I would expect something like:
char word[40];
int nChars = scanf("%39s", word);
NSString *word2 = [[NSString alloc] initWithCString:word encoding:NSASCIIStringEncoding];
Note that initWithCString per design only supports properly null '\0' terminated 8-bit character arrays. For unterminated bytes arrays you have initWithBytes:length:encoding: instead.
For Unicode characters you could consider initWithCharactersNoCopy:length:freeWhenDone:.
I want a input from user their name and output that input name in NSLog using NSString.
I don't know which % sign and how to output that.
Can i use scanf() function for that?
Please help me , i am just beginner of Objective-C.
You can use %# for all objects including NSString. This will in turn call the objects description method and print the appropriate string. Most objects have a rather useful representation already there (e.g. NSArray objects return the descriptions of all their contents).
Mark Dylan is the name which would be stored in the Name variable.
NSString* Name = #"Mark Dylan";
This code will allow you to ask their name and scan it into memory which will be stored in the Name variable.
NSLog(#"What is your name?");
scanf("%#", &Name);
If you want to print out the variable you can use;
NSLog(#"Your name is %#", Name);
%# is what you want. It fit for object like NSString, [YourViewController class]
To get input from the user use a UITextField or a NSTextField. To output a string to the log file you can use NSLog, ie:
NSString* userName = #"Zawmin";
NSLog(#"name = %#", userName);
NSLog accepts a format string, so you can do something like this:
#include <stdio.h>
#include <Foundation/Foundation.h>
// 1024 characters should be enough for a name.
// If you want something more flexible, you can use GNU readline:
// <http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html>
#define MAX_NAME_LENGTH 1024
// Get name from user input
char name[MAX_NAME_LENGTH];
name[0] = '\0'; // just in case fgets fails
fgets(name, MAX_NAME_LENGTH, stdin);
// Put name into NSString object and output it.
NSString *name = [NSString stringWithUTF8String:name];
NSLog(#"%#", name);
%# works for all Objective-C objects.
If you want to output a C-string (char* or const char*), use %s. Never put a non-literal string as the first argument to NSLog as this opens security holes.
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);
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.
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:].
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.
This is how I'd do it:
char word [40];
scanf("%s",word);
NSString * userInput = [[NSString alloc] initWithCString: word encoding: NSUTF8StringEncoding];
yes, but sscanf does, and may be a good solution for complex NSString parsing.
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);
Simple Solution is
char word[40];
scanf("%39s", word);
NSString* word2 = [NSString stringWithUTF8String:word];
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];