NSString

1.初始化

char *str1="C string";//这是C语言创建的字符串
NSString *str2=@"OC string";//ObjC字符串需要加@,并且这种方式创建的对象不需要自己释放内存
//下面的创建方法都应该释放内存
NSString *str3=[[NSString alloc] init];
str3=@"OC string";
NSString *str4=[[NSString alloc] initWithString:@"Objective-C string"];
NSString *str5=[[NSString alloc] initWithFormat:@"age is %i,name is%.2f",19,1.72f];
NSString *str6=[[NSString alloc] initWithUTF8String:"C string"];//C语言的字符串转换为ObjC字符串
//以上方法都有对应静态方法(一般以string开头),不需要管理内存(系统静态方法一般都是自动释放)
NSString *str7=[NSString stringWithString:@"Objective-C string"];

2.字符串的大小写和比较

NSLog(@""Hello world!" to upper is %@",[@"Hello world!" uppercaseString]); //结果:"Hello world!" to upper is HELLO WORLD!
NSLog(@""Hello world!" to lowwer is %@",[@"Hello world!" lowercaseString]); //结果:"Hello world!" to lowwer is hello world!
//首字母大写,其他字母小写
NSLog(@""Hello world!" to capitalize is %@",[@"Hello world!" capitalizedString]);
//结果:"Hello world!" to capitalize is Hello World!
BOOL result= [@"abc" isEqualToString:@"aBc"];
NSLog(@"%i",result);
//结果:0
NSComparisonResult result2= [@"abc" compare:@"aBc"];//如果是[@"abc"caseInsensitiveCompare:@"aBc"]则忽略大小写比较
if(result2==NSOrderedAscending){//-1实际上是枚举值
NSLog(@"left<right.");
}else if(result2==NSOrderedDescending){//1
NSLog(@"left>right.");
}else if(result2==NSOrderedSame){//0
NSLog(@"left=right."); }
//结果:left>right.
}

3.截取和匹配

NSLog(@"has prefix ab? %i",[@"abcdef" hasPrefix:@"ab"]);
//结果:has prefix ab? 1   YES 头部匹配
        
NSLog(@"has suffix ab? %i",[@"abcdef" hasSuffix:@"ef"]);
//结果:has suffix ab? 1   NO  尾巴匹配
        
NSRange range=[@"abcdefabcdef" rangeOfString:@"cde"];//注意如果遇到cde则不再往后面搜索,如果从后面搜索或其他搜索方式可以设置第二个options参数
if(range.location==NSNotFound){
      NSLog(@"not found.");
}
else{
      NSLog(@"range is %@",NSStringFromRange(range));
}
//结果:range is {2, 3}

4.字符串的分割

NSLog(@"%@",[@"abcdef" substringFromIndex:3]);
//结果:def //从index＝3开始直到末尾，包含index＝3
        
NSLog(@"%@",[@"abcdef" substringToIndex:3]);
//结果:abc //从index＝0开始直到index＝3，但是不包含index＝3
        
NSLog(@"%@",[@"abcdef" substringWithRange:NSMakeRange(2, 3)]);
//结果:cde
        
NSString *str1=@"12.abcd.3a";
NSArray *array1=[str1 componentsSeparatedByString:@"."];
//字符串分割
NSLog(@"%@",array1);
//
(
    12,
    abcd,
    3a
)

5.其他

NSLog(@"%i",[@"12" intValue]);//类型转换
//结果:12
        
NSLog(@"%zi",[@"hello world,世界你好!" length]);//字符串长度注意不是字节数
//结果:17
        
NSLog(@"%c",[@"abc" characterAtIndex:0]);//取出制定位置的字符
//结果:a
        
const char *s=[@"abc" UTF8String];//转换为C语言字符串
NSLog(@"%s",s);
//结果:abc
 