NSString的使用

创建常量字符串
创建空字符串
initWithString方法
用标准C创建字符串
创建格式化字符串
创建临时字符串
从文件创建字符串
用字符串创建字符串，并写入到文件
用C比较:strcmp函数
isEqualToString方法
compare方法
不考虑大小写比较字符串
输出大写或者小写字符串
rangeOfString:方法
substringToIndex:方法
substringFromIndex:
substringWithRange:
stringWithCapacity:
appendString:和appendFormat:
insertString:atIndex:方法
setString: 方法
replaceCharactersInRange: withString:
hasPrefix: 和hasSuffix:

1、从文件创建字符串

创建常量字符串

NSString*aString = @”This is a String”;
NSLog(@”string = %@”,aString);
打印：sring ＝ThisisaString

创建空字符串，给予赋值

NSString *aString = [[NSString  alloc]  init];
aString = @”This is a String”;
NSLog(@”string = %@”,aString);
打印：sring ＝ThisisaString

initWithString方法

作用：相对上面的方法可提升速度
NSString *astring = [[NSString  alloc]  initWithString:@"This is aString!"];

用标准C创建字符串

方法：initWithCString
char *cString = ”This is a String”;
NSString *astring = [[NSString  alloc]  initWithCString:Cstring];
NSLog(@”string = %@”,aString);
打印：sring ＝ThisisaString

创建格式化字符串

占位符：由一个％加一个字符组成。
inti = 1;
intj = 2;
 NSString *aString= [[NSString  alloc]  initWithString:[NSString  stringWithFormat:@“i is %d, j is %d”,i,j]];
NSLog(@”string = %@”,aString);
打印：string=i is 1, j is 2

创建临时字符串

NSString *aString;
aString= [NSString  stringWithCString:“Thisis a temporary string”];
NSLog(@”aString = %@”,aString);
打印：aString = This is a temporary string

从文件创建字符串

获取文件路径
NSString*path = [[NSBundle mainBundle]  pathForResource:@“aString.text”ofType:nil];
NSString*aString= [[NSString  alloc]  initWithContentsOfFile:path];

2、用字符串创建字符串，并写入到文件

用字符串创建字符串
NSString*aString = [[NSString  alloc]  initWithString:@“Thisis a String!”];
保存到的文件
NSString*path = @“astring.text”;
写入文件
[aString writeToFile: path atomically: YES];

3、用C比较:strcmp函数

char string1[] = “string!”;
 char string2[] =“string!”;
 if(strcmp(string1, string2) == 0) {
  NSLog(@“1”);
}
说明：strcmp()用来比较字符串（区分大小写），其原型为：    intstrcmp(constchar *s1,constchar *s2);

4、isEqualToString方法

比较两个字符串是否相等，返回布尔类型BOOL
NSString *aString01= @“This is a String!”;
 NSString *aString02= @“This is a String!”;
BOOL result = [aString01  isEqualToString:aString02];

5、compare方法

comparer返回的三种值：
NSOrderedSame判断两者内容是否相同
NSOrderedAscending判断两对象值的大小(按字母升序进行比较，aString02大于aString01为真)
NSOrderedDescending判断两对象值的大小(按字母将序进行比较，aString02小于aString01为真)

NSOrderedSame判断两者内容是否相同
NSString *aString01= @“This is a String!”;
NSString*aString02= @“This is a String!”;
 BOOL result = [aString01 compare:aString02] ==NSOrderedSame;
if (result){
  //为真
  NSLog(@”真”);
}

NSOrderedAscending判断两对象值的大小(按字母顺序进行比较，aString02大于aString01为真)
NSString *aString01= @"This is aString!";
NSString*aString02= @"this is aString!";
BOOL result = [aString01  compare:aString02] ==NSOrderedAscending;
if (result){
  //为真
  NSLog(@”真”);
}

NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，aString02小于aString01为真)
NSString *aString01= @"this is a String!";
NSString *aString02= @"This is aString!";
BOOL result = [aString01 compare:aString02] ==NSOrderedDescending;
if (result){
  //为真
  NSLog(@”真”);
}

6、不考虑大小写比较字符串

NSString *astring01 = @"this is a String!";
NSString*astring02 = @"This is a String!";
 BOOL result = [astring01  caseInsensitiveCompare:astring02] ==NSOrderedSame;
 //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)

NSString *astring01 = @"this is a String!";
 NSString *astring02 = @"This is a String!";
 BOOL result = [astring01  compare:astring02options:NSCaseInsensitiveSearch |NSNumericSearch] ==NSOrderedSame;
//NSCaseInsensitiveSearch:不区分大小写比较NSLiteralSearch:进行完全比较，区分大小写NSNumericSearch:比较字符串的字符个数，而不是字符值。

7、输出大写或者小写字符串

NSString *string1 = @"AString";
NSString *string2 = @"String";

NSLog(@"string1:%@",[string1 uppercaseString]);//大写
打印：string1: A STRING

NSLog(@"string2:%@",[string2 lowercaseString]);//小写
打印：string2: string

NSLog(@“string2:%@”,[string2 capitalizedString]);//首字母大写
打印：String


#### 8、rangeOfString:方法

查找字符串某处是否包含其它字符串。
NSString string1 =@“This is astring”;
NSStringstring2 =@“string”;
NSRange range = [string1 rangeOfString:string2];
intlocation = range.location;//字符串所在位置
NSString*aString= [[NSString alloc] initWithString:[NSString stringWithFormat:@“Location:%i,Leight:%i”,location,leight]];
NSLog(@”aString:%@",aString);
打印：aString:Location:10,Leight:6


#### 9、substringToIndex:方法

从字符串的开头一直截取到指定的位置，但不包括该位置的字符。
NSString string1 =@“This is astring”;
NSStringstring2 = [string1 substringToIndex:3];
NSLog(@"string2:%@",string2);
打印：string2: Thi


#### 10、substringFromIndex:

以指定位置开始（包括指定位置的字符），并包括之后的全部字符。
NSString *string1 =@“This is astring”;
NSString *string2 = [string1 substringFromIndex:3];
NSLog(@“string2:%@”,string2);
打印：string2: s is a string


#### 11、substringWithRange:

按照所给出的位置，长度，任意地从字符串中截取子串。
NSString string1 =@“This is astring”;
NSStringstring2 = [string1 substringWithRange:NSMakeRange(0, 4)];
NSLog(@“string2:%@”,string2);


#### 12、stringWithCapacity:

按照固定长度生成空字符串。
NSMutableString *String;
String = [NSMutableString stringWithCapacity:40];
这是初始化一个可变的字符串


#### 13、appendString:和appendFormat:

把一个字符串接在另一个字符串的末尾。
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is aNSMutableString"];
[String1 appendString:@", Yes"];
[String1 appendFormat:[NSString stringWithFormat:@",it is"]];
NSLog(@"String1:%@",String1);
打印：String1: :This isaNSMutableString, Yes, it is


#### 14、insertString:atIndex:方法

在指定位置插入字符串。
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@“This is a NSMutableString”];
[String1 insertString:@“Hi!” atIndex:0];//在第0个位置插入
NSLog(@“String1:%@”,String1);
打印：String1: Hi! This is a NSMutableString


#### 15、setString: 方法

替换原来的值。
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 setString:@"Hello Word!"];
NSLog(@“String1:%@”,String1);
打印：String1: Hello Word!


#### 16、replaceCharactersInRange: withString:

用指定字符串替换字符串中某指定位置、长度的字符串。
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@“This is a NSMutableString”];
[String1 replaceCharactersInRange:NSMakeRange(0, 4)withString:@“That”]; //从第0个位置开始长度是4（This）用That来替换
NSLog(@“String1:%@”,String1);
打印：String1: That is a NSMutableString


#### 17、hasPrefix: 和hasSuffix:

>检查字符串是否以另一个字符串开头和是否以一个字符串结尾。
NSString *String1 =@“NSStringInformation.txt”;

[String1 hasPrefix:@“NSString”] == 1 ? NSLog(@“YES”): NSLog(@“NO”);
打印：YES

[String1 hasSuffix:@“.txt”]= = 1 ? NSLog(@“YES”): NSLog(@“NO”);
打印：YES

说明：用到的“？：” 是三目运算符