开发过程中，我们会遇到很多关于字符串的操作，它是一个常用的数据类型，下面对它的用法进行了汇总：
//1、创建常量字符串。 NSString *astring = @"This is a String!"; //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); NSString *path = @"astring.text"; NSString *astring = [[NSString alloc] initWithContentsOfFile:path]; NSLog(@"astring:%@",astring); [astring release]; NSString *astring = [[NSString alloc] initWithString:@"This is a String!"]; NSLog(@"astring:%@",astring); NSString *path = @"astring.text"; [astring writeToFile: path atomically: YES]; [astring release]; //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)
//如何判断字符串为空
NSString *urlString = [urlInput stringValue];
if (!urlString) { NSLog( @”NO INPUT.” ); } else { if ([urlString length] == 0 ) { NSLog( @”NO INPUT.” ); } else { } } }