OC语言基础之NSString

1.字符串的创建

NSString *s1 = @"jack";

   //NSString *s2 = [[NSString alloc] initWithString:@"jack"];

   NSString *s3 = [[NSString alloc] initWithFormat:@"age is %d", 10];

   // C字符串 --> OC字符串
   NSString *s4 = [[NSString alloc] initWithUTF8String:"jack"];
   // OC字符串 --> C字符串
   const char *cs = [s4 UTF8String];

   // NSUTF8StringEncoding 用到中文就可以用这种编码
   NSString *s5 = [[NSString alloc] initWithContentsOfFile:@"/Users/apple/Desktop/1.txt" encoding:NSUTF8StringEncoding error:nil];

/*
     一般都会有一个类方法跟对象方法配对
     [NSURL URLWithString:<#(NSString *)#>];
     [NSString stringWithFormat:@""];
     [NSString stringWithContentsOfFile:<#(NSString *)#> encoding:<#(NSStringEncoding)#> error:<#(NSError *__autoreleasing *)#>];

     */

2.常用方法

1）检查前缀

NSString *str = @"qq=12344&pwd=adadfs";
   [str hasPrefix:@"qq="];

   [str hasSuffix:@"fs"];

2）大小写转换

    NSString *str = [@"adbDAd" lowercaseString];
    NSString *upStr = [str uppercaseString];
    NSLog(@"%@", upStr);
    //    [[@"adbDAd" lowercaseString] isEqualToString:@"adsfasd"];

3）可变字符串

   NSMutableString *str = [[NSMutableString alloc] initWithCapacity:0];

    [str appendFormat:@"123"];  //123
    //    NSLog(@"%@", str);
    //
    //    NSString *str1 = @"123";
    //    NSString *str2 = [str1 stringByAppendingString:@"aaaa"];
    //    NSLog(@"%@", str2);
    //
    NSRange rang3 = [str rangeOfString:@"3"];
    [str deleteCharactersInRange:rang3];
    NSLog(@"%@", str);

    [str insertString:@"aaa" atIndex:0];

    // @"3" @""
    [str replaceOccurrencesOfString:@"3"
                         withString:@""
                            options:NSLiteralSearch
                              range:NSMakeRange(0, str.length)];
    NSLog(@"%@", str);