NSString基本用法

–实例化方法————–
NSString *str = [[NSString alloc] init];
NSString *str = [[[NSString alloc] init] autorelease];

注意：在NSString 中存在自己的实例化和初始化的方法 例如：
NSString *str1 = [NSString stringWithCString:”new String” enconding: NSACIIStringEncoding];
NSString *str2 = [NSString alloc] initWithCString:”new String” enconding: NSACIIStringEncoding］；
str1和str2两个对象是相同的。

–NSStringEncoding 中常用的字符编码—————-
NSASCIIStringEncoding
NSUTF8StringEncoding
NSUnicodeStringEncoding

–NSString创建实例—————-
带“@”符号的方法只能定义含有英文和数字的NSString实例,例如:
NSString *str = “Hello money~”;
–生成含有中文的NSString方法————-
//此方法自动释放内存
+ (id)stringWithCString:(const char*)cString encoding:(NSStringEncoding)encoding;
//进行alloc后进行初始化
- (id)initWithCString:(const char*)cString encoding:(NSStringEncoding)encoding;
例如:
NSString *string = [NSString stringWithCString:”您好” encoding:NSUTF8StringEncoding];
NSString *string = [[NSString alloc] initWithCString:”您好” encoding:NSUTF8StringEncoding];

–使用格式创建字符串————-
+ (id)stringWithFormat:(NSString *)format…
- (id)initWithFormat:(NSString *)format…
例如：
NSString *str = “hello”;
NSString *string = [NSString stringWithFormat:@”%@ world”,str];
NSLog(string); 结果：hello world
–常用的替换符————–
%@ NSString实例
%d,%D,%i 整数
%u,%U 无符号整数
%x 将无符号整数以十六进制小写字母显示
%X 将无符号整数以十六进制大写字母显示
%f 小数
%c 字符
%s C语言字符串
%% 显示％字符本身

---

NSRange

–NSRange的定义
typedef struct _NSRange
{
unsigned int location;
unsigned int length;
}NSRange;

NSMakeRange函数
－－这个函数比较特殊 返回一个NSRange的对象。
NSMakeRanger(unsigned int location,unsigned int length);
例如：
NSRange range = NSMakeRanger(0,5);
NSLog(@”location is %d,length is %d”,range.location,range.length);

---

计算字符串长度
- (unsigned int)length;

---

字符串连接，插入和删除
1、连接
- (NSString )stringByAppendingString:(NSString )string;
- (NSString )stringByAppendingFormat:(NSString )format…;
例如：
NSString *str1 = @”hello”;
NSString *str2 = @”world”;
NSString *str3 = [str1 stringByAppendingString:str2];
NSString *str4 = [str2 stringByAppendingFormat:@”%d…%d”,10,20];
str4 –> world 10…20

 -----------------  NSMutableString的生成  NSString   + (id)string;  //生成空字符串的实例  + (id)stringWithString:(NSString *)string;     //带自动释放内存  - (id)initWithString:(NSString *)string;  例如:  NSMutableString *string = [NSMutableString stringWithString:@"hello"]; 

2、追加字符串
NSMutableString
+ (void)appendString:(NSString *)string;
- (void)appendFormat:(NSString *)format…;
例如：
NSMutableString string = [NSMutableString string];
[string appendString:@”hello”];
[string appendString:@”money”];
[string appendString:@” and world”];
3、插入字符串
NSMutableString
+ (void)insertString:(NSString *)string atIndex:(unsigned)index;
从index位置插入字符串
例如：
NSMutableString *string = [NSMutableString stringWithString:@”Mac X”];
[string insertString:@”OS” atIndex:4];
string –> Mac OS X
4、删除字符串
NSMutableString
+ (void)deleteCharactersInRange:(NSRange)range;
例如：
NSMutableString *string = [NSMutableString stringWithString:@”Mac os”];
[string deleteCharactersInRange:NSMakeRanger(0,1)];
NSLog(string);
string –>ac os;
5、字符串比较
NSString
- (BOOL)isEqualToString:(NSString *)string;
6、比较前置串和后置串
NSString
- (BOOL)hasPrefix:(NSString *)string;
- (BOOL)hasSuffix:(NSString *)string;
例如:
NSString *str1 = @”Mac OS”;
NSString *str2 = @”Mac Pro”;
BOOL flag;
flag = [str1 hasPrefix:@”Mac”]; YES
flag = [str2 hasSuffix:@”OS”]; NO
7、字符串检索
NSString
//如果找到就返回范围，否则NSRange的location项被设置为NSNotFound
- (NSRange)rangeOfString:(NSString *)subString;
- (NSRange)rangeOfString:(NSString *)subString option:(unsigned)mask;
- (NSRange)rangeOfString:(NSString *)subString option:(unsigned)mask range:(NSRange)range;
－－－－－mask常用选项列表
NSCaseInsensitiveSearch 不区分字母大小写
NSLiteralSearch 对字符串进行字节单位的比较，一般可提高检索速度
NSBackwardsSearch 从范围的末尾开始检索
NSAnchoredSearch 仅检索制定范围的前部。忽略字符串中间的检索字符
例如：
NSString *string = @”hello world”;
NSRange range = [string rangeOfString:@”he”];
if(range.location != NSNotFound)
{
NSLog(@” location=%d,length=%d”,range.location,range.length);
}
8、截取字符串
NSString
- (NSString *)substringToIndex:(unsigned)index; //返回字符串开头至index位的字符串 不包含索引位
- (NSString *)substringFromIndex:(unsigned)index; //返回字符串第index位至末尾的字符串 包含索引位
- (NSString *)substringWithRange:(NSRange)range; //返回字符串中范围range内的字符串 包含索引位
例如：
NSString *string = [string substringWithRange:NSMakeRange(5,2)];
9、读取文本文件
NSString
+ (id)stringWithContentsOfFile:(NSString )path usedEncoding:(NSStringEncoding )enc error:(NSError **)error //自动释放内存

 - (id)initWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error  例如：  NSString *string = [NSString stringWithContentsOfFile:@"/user/test/yw.txt" encoding:NSUTF8StringEncoding error:&error];  if(string){} 

10、输出文本文件
NSString
- (BOOL)writeToFile:(NSString )path atomically:(BOOL)useAuxiliaryFile encoding:(NSStringEncoding)enc error:(NSError *)error
//参数 atomically 暂时将文件保存到辅助文件中
//path
The file to which to write the receiver. If path contains a tilde (~) character, you must expand it withstringByExpandingTildeInPath before invoking this method.
—-下面是网上找的例子 感谢 @chenshizero
//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]);