OC_NSString的常用方法

1,字符串的简单用法：
#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

//创建常量字符串
NSString* str=@"This is a string";

//获取字符串的长度
NSUInteger len=[str length];
NSLog(@"length=%lu", len);   //result:16

//获取下标为1的字符,用unichar接收
unichar c=[str characterAtIndex:1];
NSLog(@"%c", c);     //result:h

NSLog(@"%lu", sizeof(unichar));  //result:2

//initWithString初始化字符串
str=[[NSString alloc]
initWithString:@"Hello World"];
NSLog(@"%@", str);           //result:hello world
[str release];

//用标准c字符串创建oc字符串 :initWithCString 方法
str=[[NSString alloc]
initWithUTF8String:"This is c string"];
NSLog(@"%@", str);        //result:This is c string
printf("%s\n", [str UTF8String]);

[str release];

str=[NSString stringWithString:@"Hello iOS"];
NSLog(@"%@", str);         //result Hello iOS

int age=30;
//创建格式化字符串。
str=[[NSString alloc]
initWithFormat:@"age=%d", age];
NSLog(@"%@", str);
[str release];
//stringWithFormat也可用于拼接字符串
str=[NSString stringWithFormat:@"1+1=%d", 1+1];

NSLog(@"%@", str);

[pool drain];
return 0;
}
2,从文件中读取字符串
#import <Foundation/Foundation.h>

#define PATH "/Users/lixuefeng/Desktop/dict.txt"

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

NSError* error=nil;
//下面也可用 NSString* path=[NSString stringWithUTF8String:PATH];就不用手动释放path了
NSString* path=[[NSString alloc] initWithUTF8String:PATH];

/*
下面也可用
NSString* fileContentString=
[[NSString alloc]
initWithContentsOfFile:path
encoding:NSUTF8StringEncoding
error:&error];

但是不要忘了
[fileContentString release];
*/
NSString* fileContentString=[NSString
stringWithContentsOfFile:path
encoding:NSUTF8StringEncoding
error:&error];   //如果创建失败,error改变指针指向,指向内部创建的一个NSerror对象

[path release];

if (nil!=error) {
NSLog(@"%@", error);
exit(-1);
}
NSLog(@"%@", fileContentString);

[pool drain];
return 0;
}

3,写入文件到字符串

NSString *astring = [[NSString alloc]
initWithString:@"This is a String!"];

NSLog(@"astring:%@",astring);
NSString *path = @"astring.text";
[astring writeToFile: path atomically: YES];
[astring release];

4,重写类描述方法

#import <Foundation/Foundation.h>

@interface Person : NSObject
@end

@implementation Person
#if 1
-(NSString*)description
{
return @"This is Person's object";
}
#endif
@end

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

Person* p=[[Person alloc] init];
NSLog(@"%@", p);
[p release];

[pool drain];
return 0;
}

重写了类描述方法，我们用NSLog(@"%@", p );就会调用我们自己的方法。
调试的时候覆写类描述方法比较有用
5,字符串的比较

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

NSString* str1=@"Hello World";
NSString* str2=@"hello World";

if([str1 isEqualToString:str2])
{
NSLog(@"YES");
}
else
{
NSLog(@"NO");
}
//compare方法对应的返回值为enum _NSComparisonResult {NSOrderedAscending = -1, NSOrderedSame, NSOrderedDescending};
NSComparisonResult ret=[str1 compare:str2];
if (NSOrderedAscending==ret) {
NSLog(@"%@<%@", str1, str2);
}

if (NSOrderedSame==ret) {
NSLog(@"%@=%@", str1, str2);
}

if (NSOrderedDescending==ret) {
NSLog(@"%@>%@", str1, str2);
}

[pool drain];
return 0;
}

6，字符串的截取

#import <Foundation/Foundation.h>

NSString* MyStringFromRange(NSRange range)
{
NSString* str=[NSString
stringWithFormat:@"{%lu, %lu}",
range.location, range.length];
return str;
}
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

NSString* str1=@"this is a string";
NSString* str2=@"string";
NSRange range;
//判断一个字符串中是否包含有另外一个字符串，并返回str2再str1中得位置和长度
range=[str1 rangeOfString:str2];

if(range.location!=NSNotFound) //
{
#if 0
NSLog(@"loc:%lu, len:%lu",
range.location, range.length );
#endif
//NSLog(@"%@", NSStringFromRange(range));
NSLog(@"%@", MyStringFromRange(range));
}

//iPhone, iPad, iTV, iOS, iMac
str1=@"Hello, iOS";
//判断字符串中是否包含前缀或着后缀。
[str1 hasPrefix:@"Hello"] == YES ?NSLog(@"YES Hello") : NSLog(@"NO");
[str1 hasSuffix:@"iOS"] == YES ?NSLog(@"YES iOS") : NSLog(@"NO");

//截取字符串
//-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
//-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
//-substringWithRange: //按照所给出的位置，长度，任意地从字符串中截取子串
str2=[str1 substringFromIndex:7];
NSLog(@"%@", str2);
NSLog(@"%@", str1);

str2=[str1 substringToIndex:5];
NSLog(@"%@", str2);

//range=(NSRange){3, 2};
range=NSMakeRange(3, 2);
str2=[str1 substringWithRange:range];
NSLog(@"%@", str2);

[pool drain];
return 0;
}

运行结果：

2012-06-24 13:33:46.107 demo8[1606:707] {10, 6}
2012-06-24 13:33:46.109 demo8[1606:707] YES Hello
2012-06-24 13:33:46.110 demo8[1606:707] YES iOS
2012-06-24 13:33:46.111 demo8[1606:707] iOS
2012-06-24 13:33:46.111 demo8[1606:707] Hello, iOS
2012-06-24 13:33:46.112 demo8[1606:707] Hello
2012-06-24 13:33:46.112 demo8[1606:707] lo