objective-c 中NSString的用法

1、创建常量字符串

     NSString *aString = @"hello";

2、创建空字符串，给予赋值

    NSString *astring = [[NSString alloc] init];
    astring = @"This is a String!";
    NSLog(@"astring:%@",astring);
    [astring release];

3、在以上方法中，提升速度:initWithString方法
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
    NSLog(@"astring:%@",astring);
    [astring release];

4、用标准c创建字符串:initWithCString方法
    char *Cstring = "This is a String!";
    NSString *astring = [[NSString alloc] initWithCString:Cstring];
    NSLog(@"astring:%@",astring);
    [astring release];

5、创建格式化字符串:占位符（由一个%加一个字符组成）
    int i = 1;
    int j = 2;
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"%d.This is %i string!",i,j]];
    NSLog(@"astring:%@",astring);
    [astring release];

6、创建临时字符串
    NSString *astring;
    astring = [NSString stringWithCString:"This is a temporary string"];
    NSLog(@"astring:%@",astring);

/*----------------从文件读取字符串:initWithContentsOfFile方法----------------*/    
    NSString *path = @"astring.text";
    NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
    NSLog(@"astring:%@",astring);
    [astring release];

/*----------------写字符串到文件:writeToFile方法----------------*/    
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
    NSLog(@"astring:%@",astring);
    NSString *path = @"astring.text";    
    [astring writeToFile: path atomically: YES];
    [astring release];   
 /*----------------比较两个字符串----------------*/        
    //用C比较:strcmp函数
 
    char string1[] = "string!";
    char string2[] = "string!";
    if(strcmp(string1, string2) = = 0)
    {
        NSLog(@"1");
    }
 
 
    //isEqualToString方法    
    NSString *astring01 = @"This is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 isEqualToString:astring02];
    NSLog(@"result:%d",result);
 
 
    //compare方法(comparer返回的三种值)    
    NSString *astring01 = @"This is a String!";
    NSString *astring02 = @"This is a String!";    
    BOOL result = [astring01 compare:astring02] = = NSOrderedSame;    
    NSLog(@"result:%d",result);    
    //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] = = NSOrderedAscending;    
    NSLog(@"result:%d",result);
    //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 a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 compare:astring02] = = NSOrderedDescending;    
    NSLog(@"result:%d",result);     
    //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)
 
 
    //不考虑大小写比较字符串1
    NSString *astring01 = @"this is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 caseInsensitiveCompare:astring02] = = NSOrderedSame;    
    NSLog(@"result:%d",result);     
    //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)
 
 
    //不考虑大小写比较字符串2
    NSString *astring01 = @"this is a String!";
    NSString *astring02 = @"This is a String!";
    BOOL result = [astring01 compare:astring02
                            options:NSCaseInsensitiveSearch | NSNumericSearch] = = NSOrderedSame;    
    NSLog(@"result:%d",result);     
 
    //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。
 
 
    /*----------------改变字符串的大小写----------------*/    
 
    NSString *string1 = @"A String";
    NSString *string2 = @"String";
    NSLog(@"string1:%@",[string1 uppercaseString]);//大写
    NSLog(@"string2:%@",[string2 lowercaseString]);//小写
    NSLog(@"string2:%@",[string2 capitalizedString]);//首字母大小
 
 
    /*----------------在串中搜索子串----------------*/        
 
    NSString *string1 = @"This is a string";
    NSString *string2 = @"string";
    NSRange range = [string1 rangeOfString:string2];
    int location = range.location;
    int leight = range.length;
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];
    NSLog(@"astring:%@",astring);
    [astring release];
 
 
    /*----------------抽取子串 ----------------*/        
 
    //-substringToIndex: 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 a string";
    NSString *string2 = [string1 substringToIndex:3];
    NSLog(@"string2:%@",string2);
 
 
    //-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 a string";
    NSString *string2 = [string1 substringFromIndex:3];
    NSLog(@"string2:%@",string2);
 
 
    //-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 a string";
    NSString *string2 = [string1 substringWithRange:NSMakeRange(0, 4)];
    NSLog(@"string2:%@",string2);
 
 
    //扩展路径
 
    NSString *Path = @"~/NSData.txt";
    NSString *absolutePath = [Path stringByExpandingTildeInPath];
    NSLog(@"absolutePath:%@",absolutePath);
    NSLog(@"Path:%@",[absolutePath stringByAbbreviatingWithTildeInPath]);
 
 
 
    //文件扩展名
    NSString *Path = @"~/NSData.txt";
    NSLog(@"Extension:%@",[Path pathExtension]);