利用函数 writeTOFile

NSError * error = nil;
NSString * string = @"输入的文字";
NSString * path = @"文件路径";

BOOL isSucc = [string writeToFile:path atomically:YES 
			encoding:NSUTF9StringEncodeing error:&error];
if (isSucc){
	NSLog(@"写入成功");
}else{
	NSLog(@"写入失败");
}