OC语言--字符串(NSString& NSMutableString)

首先声明一下:

OC 中的函数，是全局的，如 NSLog（）；，它不属于任何类，不属于任何一个对象。

OC 中的方法，非全局的，init 方法，用中括号来使用，它属于类本身，或者属于对象本身；分为类方法，和实例方法（对象方法）；方法被封装对象，或类模板当中

1. 不可变字符串NSString

1.1 OC字符串和C字符串的不同

OC字符串是对象，占用堆空间；C 字符串是数据，它占用栈空间

1.2 OC字符串的常见操作

(1) 常用创建方法

//实例方法创建字符串

- (instancetype)initWithString:(NSString *)aString；

- (instancetype)initWithFormat:(NSString *)format, …;

- (instancetype)initWithUTF8String:(const char *)bytes;

//用类方法创建字符串

+ (instancetype)stringWithString:(NSString *)aString；

+ (instancetype)stringWithFormat:(NSString *)format,, …；

+ (instancetype)stringWithUTF8String:(const char *)bytes；

(2)求字符串长度

- (NSUInteger)length;

(3) 通过索引获取相应的字符

- (unichar)characterAtIndex:(NSUInteger)index;

(4) 字符串比较

//判断两个字符串是否相等 

- (BOOL)isEqualToString:(NSString *)aString；

//比较两个字符串大小

- (NSComparisonResult)compare:(NSString *)aString；

//不区分大小写比较大小

- (NSComparisonResult)caseInsensitiveCompare:(NSString *)aString;

(5) 字符串查找//在给定的字符串中去查找子字符串

- (NSRange)rangeOfString:(NSString *)aString;

(6) 判断前后缀

//前缀字符串

- (BOOL)hasPrefix:(NSString *)aString;

//后缀字符串

- (BOOL)hasSuffix:(NSString *)aString;

(7) 数字字符串转化为各种数字类型

- (double)doubleValue;

- (float)floatValue;

- (int)intValue;

//long unsigned int

- (NSInteger)integerValue;

- (long long)longLongValue;

- (BOOL)boolValue;  

(8) 大小写转换

- (NSString *)uppercaseString;//将所有字符转换成大写

- (NSString *)lowercaseString;//将所有字符转换成小写

- (NSString *)capitalizedString;////将第一个字符转换成大写

*(9)字符串提取

- (NSString *)substringFromIndex:(NSUInteger)from;

- (NSString *)substringToIndex:(NSUInteger)to;

- (NSString *)substringWithRange:(NSRange)range;

*(10) 从本地读取文件内容

- (id)initWithContentsOfFile:(NSString *)path 

encoding:(NSStringEncoding)enc 

error:(NSError **)error;

+ (id)stringWithContentsOfFile:(NSString *)path 

encoding:(NSStringEncoding)enc 

error:(NSError **)error;

eg.NSString基本使用

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

  @autoreleasepool {
    NSString* a = [[NSString alloc]initWithString:@"你好吗，hello"];
    NSString* aa = [NSString stringWithFormat:@"%d %@",20,@"world"];
    NSMutableString* b = [[NSMutableString alloc]initWithString:@"HELLO"];
    unichar myChar = [a characterAtIndex:2];
    
    NSLog(@"The Length:%lu",[a length]);
    NSLog(@"The Length:%lu",[aa length]);
    NSLog(@"The Length:%lu",[b length]);
    
    NSLog(@"The character: %C",myChar);
    
    NSString* aaa = a;
    //判断是否相同
    if([a isEqualToString:aaa] == YES){
      printf("a isEqualToString aaa
");
    }else{
      printf("a is different from aaa
");
    }
    //比较字符串大小
    if([a caseInsensitiveCompare:aa] == NSOrderedSame){
      printf("a equals aaa
");
    }else if ([a caseInsensitiveCompare:aa] == NSOrderedAscending){
      printf("a less than aaa
");
    }else{//NSOrderedDescending
      printf("a great than aaa
");
    }
    
  }
    return 0;
}

2 可变字符串NSMutableString

2.1 什么是可变字符串

可变字符串对象的内容可以改变

2.2 NSMutableString 和NSString 的关系

NSMutableString 继承于 NSString，

NSString类的所有方法NSMutableString都可以使用

2.3 可变字符串常见操作

(1) 指定索引插入子串

  - (void)insertString:(NSString *)aString 

atIndex:(NSUInteger)loc;

(2) 删除指定范围的子串

- (void)deleteCharactersInRange:(NSRange)range;

(3) 追加子串

- (void)appendString:(NSString *)aString;

(4) 追加格式化子串

- (void)appendFormat:(NSString *)format, ...;

(5) 修改子串

- (void)setString:(NSString *)aString;

eg.NSMutableString基本使用

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

  @autoreleasepool {
    NSString* a = [[NSString alloc]initWithString:@"HELLO"];
    NSString* sub = [[NSString alloc]initWithString:@"EL"];
    
    NSRange myRange = [a rangeOfString:sub];
    
    printf("myRange.location:%lu
",myRange.location);
    printf("myRange.length:%lu
",myRange.length);
    
      //前缀存在判断
      //NSString* b = [NSString stringWithString:a];
    if ([a hasPrefix:@"HEL"]) {
      printf("has Prefix.
");
    }else{
      printf("has not Prefix.
");
    }
    
      //数字字符串转换成相应的数字类型
    NSString* c = [NSString stringWithUTF8String:"654321"];
    NSLog(@"Number:%d",[c intValue]+100);
      //- (BOOL)boolValue;使用
    NSString* d = [NSString stringWithFormat:@"no"];
    NSLog(@"%s",[d boolValue]?"yes":"no");
      //- (NSString *)uppercaseString;
      //将所有字符转换成大写
    NSLog(@"%@",[d uppercaseString]);
      //- (NSString *)lowercaseString;
      //将所有字符转换成小写
    NSLog(@"%@",[d lowercaseString]);
      //- (NSString *)capitalizedString;
      //将第一个字符转换成大写
    NSLog(@"%@",[d capitalizedString]);
      //-----------------------------
    NSString* longString = [NSString stringWithFormat:@"ABCDEFG1234567890"];
      //   - (NSString *)substringFromIndex:(NSUInteger)from;
    NSLog(@"%@",[longString substringFromIndex:6]);
      //- (NSString *)substringToIndex:(NSUInteger)to;
  //substringToIndex不包含index位置的字符本身
    NSLog(@"%@",[longString substringToIndex:6]);
      //- (NSString *)substringWithRange:(NSRange)range;
    NSRange myRange2 = {5,6};
    myRange2.location = 4;
    myRange2.length = 7;
    NSLog(@"%@",[longString substringWithRange:myRange2]);
    

  }
    return 0;
}