dup | 易学教程

每周一个 Python 标准库 | copy

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技术博客：https://github.com/yongxinz/tech-blog 同时，也欢迎关注我的微信公众号 AlwaysBeta ，更多精彩内容等你来。 copy 模块包括两个功能， copy() 和 deepcopy() ，用于复制现有对象。浅拷贝 copy() 创建的浅表副本是一个新容器，是对原始对象内容的引用。 import copy import functools @functools . total_ordering class MyClass : def __init__ ( self , name ) : self . name = name def __eq__ ( self , other ) : return self . name == other . name def __gt__ ( self , other ) : return self . name > other . name a = MyClass ( 'a' ) my_list = [ a ] dup = copy . copy ( my_list ) print ( ' my_list:' , my_list ) print ( ' dup:' , dup ) print ( ' dup is my_list:' , ( dup is my_list ) ) print ( '

汇编语言第七、八章总结

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and和or指令 1. and指令——逻辑与指令，按位进行与运算，通过该指令可将操作对象的相应位设为0，其他位不变 2. or指令——逻辑或指令，按位进行或运算，通过该指令可将操作对象的相应位设为1，其他位不变以字符形式给出的数据 1. 以“...”的方式指明数据是以字符的形式给出的，编译器把它们转化为相应的ASCII码大小写转换的问题 1. 大写字母+20H=小写字母；小写字母-20H=大写字母 2. and al,11011111B 可将小写字母变为大写字母；or al,00100000B 可将大写字母变为小写字母 [bx+idata] 1. 表示一个内存单元，它的偏移地址为(bx)+idata（bx中的数值加上idata） si和di 1. 是和bx功能相近的寄存器，但是si和di不能够分成两个8位寄存器来使用 [bx+si]和[bx+di] 1. [bx+si]表示一个内存单元，它的偏移地址为(bx)+(si)（即bx中的数值加上si中的数值） [bx+si+idata]和[bx+di+idata] 1. [bx+si+idata]表示一个内存单元，它的偏移地址为(bx)+(si)+idata（即bx中的数值加上si中的数值再加上idata）（一般来说，在需要暂存数据的时候，我们都应该使用栈） bx、si、di和bp 1. 只有这四个寄存器可以用在[...

Redirect stdout from python for C calls

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问题 This is a follow up question from here specifically concerning its answer. From a python module I am calling a Hello World executable that simply prints Hello World to the stdout. I am interested in redirecting that output to a python StringIO and ran into this answer which almost brings me all the way to the solution. The critical part of this answer is this code segment: 1. def redirect_stdout(): 2. print "Redirecting stdout" 3. sys.stdout.flush() # <--- important when redirecting to files

Simple http generic server using fork and dup

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问题 I'm trying to write a very basic HTTP server. I want to separate the server and the service in two separate executable (similar to inetd). So I have a generic server, that forks a service and execute its code using exec. The main loop is as follows: while(true) { int client_sock; if ((client_sock = accept(server_sock, (struct sockaddr *) NULL, NULL)) < 0) { return -1; } pid_t pid = fork(); if (pid == 0) { close(server_sock); close(0); dup(client_sock); close(1); dup(client_sock); execvp(argv

Strange behaviour when redirecting stdout in C

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问题 I'm trying to redirect stdout to a file and then restore it back to original in C, but I'm facing the following strange issue - the following piece of code succesfully writes in stdout in stdout in stdout and in file in the respective file which is all OK. #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #define STDOUT 1 int main(int argc, char* argv[]){ printf("in stdout \n"); int old_out = dup(STDOUT); close(STDOUT); int fd = open("./redirected",O_CREAT|O_RDWR|O_TRUNC,0777); printf

C Shell hanging when dealing with piping

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问题 I'm working on a C shell and am having trouble with getting an arbitrary amount of pipes to work. When I run the shell, it hangs on any piping. For some reason, when I do ls -la | sort , it hangs on the sort until I enter stuff and hit Ctrl + D . I know it has something to do with a pipe not closing, but the print statements show that pipes 3,4,5 all get closed in both the parent and child. I've been at this for a few hours and don't know why this doesn't work. Any help would be much

How to redirect the output of system() to a file?

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问题 In this C program #include <stdio.h> #include <fcntl.h> int main() { int file = open("Result", O_CREAT|O_WRONLY, S_IRWXU); dup2(stdout, file); system("ls -l"); return 0; } I'm trying to redirect the output of system() to a file, for that i have used dup2 but it is not working. What's wrong with this code ? and, please tell me if there is any better way to do this ? (without using > at the terminal ) 回答1: stdout is a FILE * pointer of the standard output stream. dup2 expects file descriptor,

数据处理的两个基本问题

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计算机是进行数据处理，运算的机器，所以存在两个问题：处理的数据的位置处理的数据的长度这两个问题，必须在机器指令中给出说明（有时候是明确的，有时候是隐式的），否者计算器就无法工作。定义的描述性符号： reg（寄存器）：ax，bx，cx，dx，ah，al···sp，bp，si，di sreg（段寄存器）：ds，ss，cs，es bx，si，di和bp 总结：在8086中，只有这四个寄存器可以用在 [...] 中进行内存寻址。在 [...] 中，他们可以单个出现，或者以组合形式出现（组合中不能有其他寄存器，但可以有idata） bp的默认段地址在ss中（和bx，si，di在ds中不同）机器指令处理的数据在什么地方数据处理大致可分为三类：读取，写入，运算指令执行前，所要处理的数据可以在3个地方：cpu内部，内存，端口汇编语言中数据位置的表达立即数（idata）对于直接包含在机器指令中的数据（执行前在cpu的指令缓冲器中），在汇编语言中称为：立即数（idata）寄存器指令要处理的数据存放在寄存器中，给出对应寄存器名段地址（SA）和偏移地址（EA）内存中的数据，通过SA+EA给出数据位置寻址方式定位内存单元的方法，即称为寻址方式指令要处理的数据有多长前面将到分为隐式给出和显式给出，例如通过寄存器和push，pop等方法就是隐式给出。

Ruby dup/clone recursively

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问题 I have a hash like: h = {'name' => 'sayuj', 'age' => 22, 'project' => {'project_name' => 'abc', 'duration' => 'prq'}} I need a dup of this hash, the change should not affect the original hash. When I try, d = h.dup # or d = h.clone d['name'] = 'sayuj1' d['project']['duration'] = 'xyz' p d #=> {"name"=>"sayuj1", "project"=>{"duration"=>"xyz", "project_name"=>"abc"}, "age"=>22} p h #=> {"name"=>"sayuj", "project"=>{"duration"=>"xyz", "project_name"=>"abc"}, "age"=>22} Here you can see the

practical examples use dup or dup2

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问题 I know what dup / dup2 does, but I have no idea when it would be used. Any practical examples? Thanks. 回答1: One example use would be I/O redirection. For this you fork a child process and close the stdin or stdout file descriptors (0 and 1) and then you do a dup() on another filedescriptor of your choice which will now be mapped to the lowest available file descriptor, which is in this case 0 or 1. Using this you can now exec any child process which is possibly unaware of your application and