NSString字符串使用

NSString是NSObject的一个子类，不同于标准的ANSI的字符串，下面大致看看这个类怎么使用。

首先安装GNUStep编译环境

编译链接代码的方式如下：

$ gcc -o test test.m -I/GNUstep/System/Library/Headers -fconstant-string-class=NSConstantString -L/GNUstep/System/Library/Libraries -lobjc -lgnustep-base

1，创建和初始化字符串

#import <Foundation/Foundation.h>

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

	//创建一个空字符串
    NSString *emptyStr = [NSString string];
    NSLog(@"%@",emptyStr);
	/*
	NSString *emptyStr2 = [[NSString alloc] init];
	NSLog(@"%@",emptyStr2);
	[emptyStr2 release];
	*/
	
	//用Byte[]数组初始化字符串
	byte bdata[4] = {'a',66,'c','d'};
	NSString *bStr = [NSString alloc];
	bStr = [bStr initWithBytes:bdata length:4 encoding:NSASCIIStringEncoding];
	NSLog(@"%@",bStr);
	[bStr release];
	
	//用unichar[]数组初始化字符串(unichar 是两个字节长的char，代表unicode的一个字符)
	unichar ucdata[4] = {'e','f','g','h'};
	NSString *ucStr = [NSString alloc];
	ucStr = [ucStr initWithCharacters:ucdata length:4];
	NSLog(@"%@",ucStr);
	[ucStr release];
	
	//用Char[]数组初始化字符串
	char cdata[5] = "abcd";
	NSString *cStr = [NSString alloc];
	cStr = [cStr initWithCString:cdata length:4];
	NSLog(@"%@",cStr);
	[cStr release];
	
	//格式化字符串
	NSString *fStr = [[NSString alloc] initWithFormat:@"Hello ciaos"];
	NSLog(@"%@",fStr);
	[fStr release];
	
	//用字符串初始化字符串
	NSString *sStr = [NSString stringWithFormat:@"%s am %d years now", "I" , 25, nil];
	NSLog(@"%@",sStr);
	
	//...
	
    [pool drain];
    return 0;
}

2，从文件读取并创建和初始化字符串

#import <Foundation/Foundation.h>

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

	//读取文件内容
	NSString *fStr = [NSString stringWithContentsOfFile:@"a.txt" encoding:NSASCIIStringEncoding error:NULL];
	NSLog(@"%@",fStr);
	
	//或者
	NSString *sStr = [[NSString alloc] initWithContentsOfFile:@"a.txt" encoding:NSASCIIStringEncoding error:NULL];
	NSLog(@"%@",sStr);
	[sStr release];
	
    [pool drain];
    return 0;
}

3，从网页读取文本并用来创建和初始化字符串

#import <Foundation/Foundation.h>

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

	//读取网页内容
	NSStringEncoding encoding;
	NSError *err = nil;
	NSString *uStr = [[NSString alloc] initWithContentsOfURL: [NSURL URLWithString:@"http://127.0.0.1/index.php"] usedEncoding:&encoding error:&err];
	NSLog(@"%@",uStr);
	[uStr release];
	
	//或者
	NSString *uStr2 = [NSString stringWithContentsOfURL: [NSURL URLWithString:@"http://127.0.0.1/index.php"] usedEncoding:&encoding error:&err];
	NSLog(@"%@",uStr2);
	
    [pool drain];
    return 0;
}

4，将字符串写入文件或URL

#import <Foundation/Foundation.h>

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

	//将字符串写入文本文件
	NSString *str = @"This should be written to file";
	BOOL res = [str writeToFile:@"b.txt" atomically:YES encoding:NSUTF8StringEncoding error:NULL];
	NSLog(@"%d",res);
	
    [pool drain];
    return 0;
}

5，获取字符串长度

#import <Foundation/Foundation.h>

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

	//字符串长度
	NSString *str = @"length of string";
	NSUInteger len = [str length];
	NSLog(@"%d",len);
	
	//按照指定编码获取长度
	unichar ucdata[4] = {'e','f','g','h'};
	NSString *str2 = [NSString alloc];
	str2 = [str2 initWithCharacters:ucdata length:4];	
	NSUInteger len2 = [str2 lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
	NSLog(@"%d",len2);	// 4
	len2 = [str2 lengthOfBytesUsingEncoding:NSASCIIStringEncoding];
	NSLog(@"%d",len2);	// 8
	[str2 release];
	
    [pool drain];
    return 0;
}

6，获取字符和字节流

#import <Foundation/Foundation.h>

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

	//获取某个字符
	NSString *str = @"Objective-C programming";
	unichar c = [str characterAtIndex:2];
	NSLog(@"%c",c);	// 'j'
	
	//获取某范围字符串
	unichar buf[10] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
	[str getCharacters:buf range:NSMakeRange(3,2)];
	NSLog(@"%c%c%c%c%c%c%c%c",buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);
	// "ec"
	
    [pool drain];
    return 0;
}

7，转换为标准ANSI字符串

#import <Foundation/Foundation.h>

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

	//获取ANSI标准字符串
	NSString *str = @"Objective-C programming";
	const char *res = [str cStringUsingEncoding:NSASCIIStringEncoding];
	NSLog(@"%s",res); // "Objective-C programming"
	
    [pool drain];
    return 0;
}

8，字符串拼接

#import <Foundation/Foundation.h>

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

	//按照指定格式拼接字符串
	NSString *str = @"Objective-C programming";
	str = [str stringByAppendingFormat:@" %s programming %s","2.0","is difficult",nil];
	NSLog(@"%@",str); // "Objective-C programming"
	
	//拼接字符串
	NSString *str1 = @"Hello ",*str2 = @"Ciaos";
	str1 = [str1 stringByAppendingString:str2];
	NSLog(@"%@",str1); // "Hello Ciaos"
	
    [pool drain];
    return 0;
}

9，字符串截取

#import <Foundation/Foundation.h>

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

	//字符串截取
	NSString *str = @"Objective-C programming";
	NSString *res = [str substringFromIndex:3];
	NSLog(@"%@",res); // "ective-C programming"
	res = [str substringWithRange:NSMakeRange(3,4)];
	NSLog(@"%@",res); // "ecti"
	res = [str substringToIndex:5];
	NSLog(@"%@",res); // "Objec"
	
    [pool drain];
    return 0;
}

10，字符串查找

#import <Foundation/Foundation.h>

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

	//字符串截取
	NSString *str = @"Objective-C programming";
	NSString *obj = @"prog";
	NSRange range = [str rangeOfString: obj];
	NSLog(@"%d %d",range.location,range.length); // 12 4
	
	obj = @"prod";
	range = [str rangeOfString: obj];
	NSLog(@"%d %d",range.location,range.length); // 2147483647 0 找不到
	
    [pool drain];
    return 0;
}

11，字符串切分

#import <Foundation/Foundation.h>

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

	//字符串切分
	NSString *str = @"apple:pear:banana";
	NSArray *arr = [str componentsSeparatedByString:@":"];
	NSLog(@"%@",arr);
	
    [pool drain];
    return 0;
}

12，NSString 和 NSMutableString 使用区别

#import <Foundation/Foundation.h>

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

	NSString *s1 = @"I am s1";
	NSString *s2 = s1;
	s2 = @"I am s2";
	NSLog(@"\ns1 = %@\ns2 = %@\n",s1,s2);
	//	s1 = I am s1
	//	s2 = I am s2
	NSLog(@"\naddr s1 = %p\naddr s2 = %p\n",s1,s2);
	//	addr s1 = 0x402000
	//	addr s2 = 0x40200c		not the same
	
	NSMutableString *ms1 = [NSMutableString stringWithString:@"I am ms1"];
	NSMutableString *ms2 = ms1;
	[ms2 setString:@"I am ms2"];
	NSLog(@"\ns1 = %@\ns2 = %@\n",ms1,ms2);
	//	s1 = I am ms2
	//	s2 = I am ms2
	NSLog(@"\naddr ms1 = %p\naddr ms2 = %p\n",ms1,ms2);
	//	addr ms1 = 0x1a53738
	//	addr ms2 = 0x1a53738	the same
	
    [pool drain];
    return 0;
}

其他——子串替换，是否包含指定前缀后缀，大小写转换等，NSString类提供了比较丰富的字符串操作函数。