ios 将NSLog日志重定向输出到文件中保存

对于那些做后端开发的工程师来说，看LOG解Bug应该是理所当然的事，但我接触到的移动应用开发的工程师里面，很多人并没有这个意识，查Bug时总是一遍一遍的试图重现，试图调试，特别是对一些不太容易重现的Bug经常焦头烂额。而且iOS的异常机制比较复杂，Objective-C的语言驾驭也需要一定的功力，做出来的应用有时候挺容易产生崩溃闪退。一遍一遍的用XCode取应用崩溃记录、解析符号，通常不胜其烦，有时还对着解析出来的调用栈发呆，因为程序当时的内部状态常常难以看明白，只能去猜测。
http://dingran.iteye.com/blog/1773573 http://blog.csdn.net/marujunyy/article/details/12005767

//
//  ZJAppDelegate.m
//  Example
//
//  Created by laizhenjie on 14-5-7.
//  Copyright (c) 2014年 Laizhenjie. All rights reserved.
//

#import "ZJAppDelegate.h"

@implementation ZJAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// Override point for customization after application launch.
[self redirectNSlogToDocumentFolder];
return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

- (void)applicationWillTerminate:(UIApplication *)application
{
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}

#pragma mark - 用户方法,将nslog的输出信息写入到dr.log文件中；
// 将NSlog打印信息保存到Document目录下的文件中
- (void)redirectNSlogToDocumentFolder
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentDirectory = [paths objectAtIndex:0];
NSString *fileName = [NSString stringWithFormat:@"dr.log"];// 注意不是NSData!
NSString *logFilePath = [documentDirectory stringByAppendingPathComponent:fileName];
// 先删除已经存在的文件
NSFileManager *defaultManager = [NSFileManager defaultManager];
[defaultManager removeItemAtPath:logFilePath error:nil];

// 将log输入到文件
freopen([logFilePath cStringUsingEncoding:NSASCIIStringEncoding], "a+", stdout);
freopen([logFilePath cStringUsingEncoding:NSASCIIStringEncoding], "a+", stderr);
}

@end