—–从文件读取字符串—–
NSString *path = @”astring.text”;
NSString *astring = [[NSString alloc] initWithContentsOfFile:path];

—–写字符串到文件—-
NSString *astring = [[NSString alloc] initWithString:@”This is a String!”];
NSString *path = @”astring.text”;
[astring writeToFile: path atomically: YES];
—–比较两个字符串—–
//1、用C比较:strcmp函数
char string1[] = “string!”;
char string2[] = “string!”;
if(strcmp(string1, string2) = = 0)
{
NSLog(@”1″);
}
//2、isEqualToString方法
NSString *astring01 = @”This is a String!”;
NSString *astring02 = @”This is a String!”;
BOOL result = [astring01 isEqualToString:astring02];
//3、compare方法(comparer返回的三种值：NSOrderedSame，NSOrderedAscending，NSOrderedDescending)
NSString *astring01 = @”This is a String!”;
NSString *astring02 = @”This is a String!”;
BOOL result = [astring01 compare:astring02] = = NSOrderedSame;   //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)
//4、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)
//5、不考虑大小写比较字符串2
NSString *astring01 = @”this is a String!”;
NSString *astring02 = @”This is a String!”;
BOOL result = [astring01 compare:astring02
options:NSCaseInsensitiveSearch | NSNumericSearch] = = NSOrderedSame;
NSLog(@”result:%d”,result);
//NSCaseInsensitiveSearch:不区分大小写比较 NSLiteralSearch:进行完全比较，区分大小写 NSNumericSearch:比较字符串的字符个数，而不是字符值。

总结一下字符串比较：可以统一使用下面函数来比较字符串， 对于进行特殊的大小比较，mask确定特殊比较的类型：例如大小写敏感、数字排序还是字符排序等等。具体见枚举类型NSStringCompareOptions的具体值。

- (NSComparisonResult)compare:(NSString *)string options:(NSStringCompareOptions)mask;

—–改变字符串的大小写—–
NSString *string1 = @”A String”;
NSString *string2 = @”String”;
NSLog(@”string1:%@”,[string1 uppercaseString]);//uppercaseString返回转换为大写的字符串
NSLog(@”string2:%@”,[string2 lowercaseString]);//lowercaseString返回转换为小写的字符串
NSLog(@”string2:%@”,[string2 capitalizedString]);//capitalizedString返回每个单词首字母大写的字符串

—–在串中搜索子串 —–

NSString *string1 = @”This is a string”;
NSString *string2 = @”string”;
NSRange range = [string1 rangeOfString:string2];
int location = range.location;
int leight = range.length;
NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];
NSLog(@”astring:%@”,astring);
[astring release];

—–抽取子串 —–

//1、-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
NSString *string1 = @”This is a string”;
NSString *string2 = [string1 substringToIndex:3];
NSLog(@”string2:%@”,string2);

//2、-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
NSString *string1 = @”This is a string”;
NSString *string2 = [string1 substringFromIndex:3];
NSLog(@”string2:%@”,string2);

//3、-substringWithRange: //按照所给出的位置，长度，任意地从字符串中截取子串
NSString *string1 = @”This is a string”;
NSString *string2 = [string1 substringWithRange:NSMakeRange(0, 4)];
NSLog(@”string2:%@”,string2);

//4、快速枚举
for(NSString *filename in direnum)    {
if([[filename pathExtension] isEqualToString:@”jpg”]){
[files addObject:filename];
}
}
    NSLog(@”files:%@”,files);//5、枚举
NSEnumerator *filenum;
filenum = [files objectEnumerator];
while (filename = [filenum nextObject]) {
NSLog(@”filename:%@”,filename);
}

@”b”,@”a”,@”e”,@”d”,@”c”,@”f”,@”h”,@”g”,nil];
NSLog(@”oldArray:%@”,oldArray);
NSEnumerator *enumerator;
enumerator = [oldArray objectEnumerator];
id obj;
while(obj = [enumerator nextObject])    {
[newArray addObject: obj];
}
[newArray sortUsingSelector:@selector(compare:)];
NSLog(@”newArray:%@”, newArray);
[newArray release];—–切分数组—–
//1、从字符串分割到数组－ componentsSeparatedByString:
NSString *string = [[NSString alloc] initWithString:@”One,Two,Three,Four”];
NSLog(@”string:%@”,string);
NSArray *array = [string componentsSeparatedByString:@","];
NSLog(@”array:%@”,array);
[string release];

//2、从数组合并元素到字符串- componentsJoinedByString:
NSArray *array = [[NSArray alloc] initWithObjects:@”One”,@”Two”,@”Three”,@”Four”,nil];
NSString *string = [array componentsJoinedByString:@","];
NSLog(@”string:%@”,string);

—–从目录搜索扩展名为jpg的文件—–
//NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *home;
home = @”../Users/”;
NSDirectoryEnumerator *direnum;
direnum = [fileManager enumeratorAtPath: home];
NSMutableArray *files = [[NSMutableArray alloc] init];
//枚举
NSString *filename;
while (filename = [direnum nextObject]) {
if([[filename pathExtension] hasSuffix:@”jpg”]){
[files addObject:filename];
}
}
//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]);

—–查找与替换—–

- (NSString *)stringByReplacingCharactersInRange  NSRange)range withString:(NSString *)replacement

- (NSString *)stringByReplacingOccurrencesOfString  NSString *)target withString:(NSString *)replacement

NSRange subRange;
subRange = [string1 rangeOfString:@"string A"];  //查找字符串string1中是否包含“string A”。返回NSRange类型。
if(subRange.location == NSNotFound)
NSLog(@”String not found “);
else  NSLog(@”string is at index %lu, length is %lu”, subRange.location, subRange.length);

Arrays 

创建一个Array：

NSString* oneString = myArray[0];
NSString* twoString = myArray[1];

  NSArray* myArray = @[@"one", @"two", @"three"];
    NSRange subArrayRange = NSMakeRange(1,2);
    NSArray* subArray = [myArray subArrayWithRange:subArrayRange];

NSArray* myArray = @[@"one", @"two", @"three"];

 NSMutableArray* myArray = [NSMutableArray arrayWithArray:
            @[@"One", @"Two", @"Three"]];

NSMutableArray* myArray = [NSMutableArray arrayWithArray:@[@"One", @"Two",
                                                               @"Three"]];

  NSDictionary* translationDictionary = @{
        @"greeting": @"Hello",
        @"farewell": @"Goodbye"

};

 NSDictionary* translationDictionary = @{@"greeting": @"Hello"};
    NSString* greeting = translationDictionary[@"greeting"];

NSMutableDictionary* aDictionary = @{};
    aDictionary[@"greeting"] = @"Hello";
    aDictionary[@"farewell"] = @"Goodbye";