iOS疯狂详解之NSFileHandle

//  创建一个文件

- (void)addField

{

NSString *documentPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];

NSString *fieldPath = [documentPath stringByAppendingPathComponent:@"student.txt"];

NSLog(@"%@",fieldPath);

NSString *txt = @"wanglong";

[txt writeToFile:fieldPath atomically:YES encoding:NSUTF8StringEncoding error:nil];

//  从路径中 读取文件 获取NSFileHandle对象

NSFileHandle *handle = [NSFileHandle fileHandleForUpdatingAtPath:fieldPath];

//  获取文件内容的 结束偏移量

unsigned long long endOffset = handle.seekToEndOfFile;

[handle seekToFileOffset:4];

//  获取当前的偏移量 初始偏移量为0

unsigned long long offset = handle.offsetInFile;

//  准备要写入的字符串

NSString *str = @"123";

NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

[handle writeData:data];

NSString *saveStr = [NSString stringWithContentsOfFile:fieldPath encoding:NSUTF8StringEncoding error:nil];

NSLog(@"%@",saveStr);

//  -------------------------------------------------------

//  覆盖数据

NSFileHandle * srcFile, * destFile; //  输入文件、输出文件

NSData * buffer;//  读取的缓冲数据

NSFileManager * manager = [NSFileManager defaultManager];

NSString * sourcePath = [documentPath stringByAppendingPathComponent:@"sourceFile.txt"];//  源文件路径

NSLog(@"%@",sourcePath);

[manager createFileAtPath:sourcePath contents:[@"Hello" dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];

NSString * destPath = [documentPath stringByAppendingPathComponent:@"destFile.txt"];//  输出文件路径

BOOL success = [manager createFileAtPath:destPath contents:[@"abcdef" dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];

if (!success) {

return;

}

srcFile = [NSFileHandle fileHandleForReadingAtPath:sourcePath];

if (!destFile) {

return;

}

destFile = [NSFileHandle fileHandleForWritingAtPath:destPath];

if (!destFile) {

return;

}

[destFile truncateFileAtOffset:0];//  将输出文件的长度设为0,(也就是将原来的文件清空)

buffer = [srcFile readDataToEndOfFile];//  读取数据

[destFile writeData:buffer];

[srcFile closeFile];

[destFile closeFile];

}