Foundation 框架之——NSString、NSMutableString 一

 1     //字符串的创建
 2     NSString *s1 = @"Rose";
 3     
 4     // 作用相当于s1，基本不用
 5     // 警告：Using ‘initWithString:‘ with a literal is redundant
 6     // 用“initWithString:“是多余的
 7     NSString *s2 = [[NSString alloc] initWithString:@"Rose"];
 8     
 9 
10      NSString *s3 = [[NSString alloc]initWithFormat:@"age  is %d",20];
11     
12     // C字符串——>OC字符串
13     // 注意"jack"前不要加@否则报错Implicit conversion of an Objective-C pointer to ‘const char *‘ is disallowed with ARC
14     // 隐式转换的objective - c指针到弧‘const char *’无效
15     NSString *s4 = [[NSString alloc] initWithUTF8String:"jack"];
16     // OC字符串——>c字符串
17     const char *cs = [s4 UTF8String];
18     
19     // NSUTF8StringEncoding 用到中文就可以用这种编码
20     NSString *s5 = [[NSString alloc]initWithContentsOfFile:@"/Users/scjy/Desktop/刘二龙练习/OC/作业/作业/图像面积/图像面积/main.m" encoding:NSUTF8StringEncoding error:nil];
21     
22     // URL ：资源路径
23     // 协议头：//路径
24     // file://
25     // ftp://
26     
27     NSURL *url = [[NSURL alloc] initWithString:@"file:///Users/scjy/Desktop/刘二龙练习/OC/作业/作业/图像面积/图像面积/main.m"];
28     NSString *s6 = [[NSString alloc]initWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];
29     
30     NSLog(@"s6:%@",s6);
31     
32    /*
33     一般都有一个类方法跟对象方法配对
34     [ NSURL URLWithString:<#(NSString *)#>];
35     [NSString stringWithFormat:<#(NSString *), ...#>];
36     [NSString stringWithContentsOfFile:<#(NSString *)#> encoding:<#(NSStringEncoding)#> error:<#(NSError *__autoreleasing *)#>];
37     
38     */