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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];

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