A detailed explanation of NSString and nsmutablestring in the Foundation framework

NSString: immutable strings

The simplest way to create a string:

NSString *str = @ "Itcast"; The string created by OC string OC is an object of the NSString class.

Char *name = "Itcast"; This is the C language string

NSLog (@ "I'm in%@ class", str);//%@ is used to output OC objects

NSLog (@ "%s", name); %s is used to output C-language strings

Benefits of using OC strings:

Manipulating strings in the form of objects;

1     // Define a string 2     @" Jack " ; 3     4     // computes the number of characters in a string and outputs the result 5     NSLog (@ "%ld", str.length);

The creation of a string:

First: Quickly create

NSString *str = @ "Jack";

The second type: Create in a formatted way

NSString *str = [[NSString alloc] Initwithformat:@ "My age is%d", +]; This is the use of object methods

NSString *str = [NSString stringwithformat:@ "My age is%d", +]; This is the use of class methods

The mutual reload between OC string and C language string

　　

1     //This is the conversion of a C-language string to a bit OC string2     Char*ch ="I love oc!";3     4NSString *str1 = [NSString stringwithutf8string:"I love oc!"];5NSString *STR2 =[NSString stringwithutf8string:ch];6NSLog (@"str1 =%@, str2 =%@", str1, str2);7     8     //This is to replace the OC string with the C language string9     Const Char*newch1 =[str1 utf8string];Ten     Const Char*NEWCH2 =[str2 utf8string]; OneNSLog (@"newch1 =%s, Newch2 =%s", Newch1, NEWCH2);

The result of the operation is:
2015-01-05 20:53:46.820 Foundation frame [444:303] str1 = I love oc!, str2 = I love oc!
2015-01-05 20:53:46.822 Foundation frame [444:303] newch1 = I love oc!, newch2 = I love oc!
Program ended with exit code:0

To read a string from a file:

NSString *str = [NSString stringwithcontentsoffile:@ "/users/mac/desktop/sb.txt" encoding:　　Nsutf8stringencoding error:nil]; This is a class method

Stringwithcontentsoffile: An absolute path is passed in later;

encoding: The following parameter is a coding method. when we want to read the string in the Chinese language when we want to use the encoding method is:nsutf8stringencoding

Error:nil indicates that if the file is not found, the returned result is null and void.

To write a string to a file:　

NSString *str = @ "I love oc!";

[@ "I love oc!" Writetofile:@ "/users/mac/desktop/sb.txt" Atomically:yes Encoding: Nsutf8stringencoding Error:nil];

[str writetofile:@ "/users/mac/desktop/sb.txt" atomically:YES encoding : nsutf8stringencoding error:nil];

The effect of the two sentences is the same.

WriteToFile: An absolute path is passed in later

atomically:YES indicates that files are only written when file creation is successful

Encoding: nsutf8stringencoding When we have Chinese, we use this coding method.

Error:nil error when returning null

Knowledge Supplement:

Protocol Header: Resource path

URL: Resource Path

file://This is the file path. When it was written here, there were three///

ftp://This is the server path.

The universal way to read a string:

　　　　

A detailed explanation of NSString and nsmutablestring in the Foundation framework