freopen - Developer IT

Equivalent of freopen in Java

- by avd

Please suggest a method to obtain a similar behaviour in Java as when we do freopen("filename","r",stdin) OR freopen("filename","w",stdout) in C.

Like freopen and scanf in c#

- by Daniel G. R.

Who knows the freopen and scanf function functionality but in c# not in c??????? thanks

using std::freopen to redirect stderr c++

So I want to redirect all stderr to a file, which is also being used by my logger for the entire time the application (game) is running. The follow redirect it away from the console, but it never appears in my file, and using fclose after the game loop is over doesnt actually do anything, where it would normally would. freopen(Logger::logFile.c_str(),"a",stderr); Any help would be great on how to get stderr to output to the text file, in a game loop.

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Cannot write the output to a text file in cpp program

- by swapedoc

I have this input file "https://code.google.com/codejam/contest/351101/dashboard/do/A-large-practice.in?cmd=GetInputFile&problem=374101&input_id=1&filename=A-large-practice.in&redownload_last=1&agent=website&csrfmiddlewaretoken=OWMxNTVmMTUyODBiYjhhN2Q2OTM3ZGJiMTNhNDkwMDF8fDEzNzIxNzI1NTE3ODAzMjA%3D" I tried to read this file :-using freopen("filename.txt",r,stdin); and then I wanted the output written to be written to another text file which I can upload in this codejam practice question for the judge. #include<iostream> #include<cstdio> using namespace std; int main() { int t,k=0,a[2000]; freopen("ab.txt","r",stdin); scanf("%d",&t); while(t--) { freopen("cb.txt","w",stdout); int c; scanf("%d",&c); int n; scanf("%d",&n); for(int i=0;i<n;i++) scanf("%d",&a[i]); printf("Case #%d: ",++k); for(int i=0;i<n-1;i++) {for(int j=i+1;j<n;j++) if((a[i]+a[j])==c) {printf("%d %d\n",i+1,j+1); i=n;} } } return 0; } This is my code. Now the problem is the output file cb.txt contains only the last line of the input. I want the the whole of the output to be written to cb.txt,so what should I do.

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Daemonize() issues on Debian

- by djTeller

Hi, I'm currently writing a multi-process client and a multi-treaded server for some project i have. The server is a Daemon. In order to accomplish that, i'm using the following daemonize() code: static void daemonize(void) { pid_t pid, sid; /* already a daemon */ if ( getppid() == 1 ) return; /* Fork off the parent process */ pid = fork(); if (pid < 0) { exit(EXIT_FAILURE); } /* If we got a good PID, then we can exit the parent process. */ if (pid > 0) { exit(EXIT_SUCCESS); } /* At this point we are executing as the child process */ /* Change the file mode mask */ umask(0); /* Create a new SID for the child process */ sid = setsid(); if (sid < 0) { exit(EXIT_FAILURE); } /* Change the current working directory. This prevents the current directory from being locked; hence not being able to remove it. */ if ((chdir("/")) < 0) { exit(EXIT_FAILURE); } /* Redirect standard files to /dev/null */ freopen( "/dev/null", "r", stdin); freopen( "/dev/null", "w", stdout); freopen( "/dev/null", "w", stderr); } int main( int argc, char *argv[] ) { daemonize(); /* Now we are a daemon -- do the work for which we were paid */ return 0; } I have a strange side effect when testing the server on Debian (Ubuntu). The accept() function always fail to accept connections, the pid returned is -1 I have no idea what causing this, since in RedHat & CentOS it works well. When i remove the call to daemonize(), everything works well on Debian, when i add it back, same accept() error reproduce. I've been monitring the /proc//fd, everything looks good. Something in the daemonize() and the Debian release just doesn't seem to work. (Debian GNU/Linux 5.0, Linux 2.6.26-2-286 #1 SMP) Any idea what causing this? Thank you

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How to decrease size of c++ source code? [closed]

- by free0u

For example #include <iostream> using namespace std; int main() { freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout); int n; cin >> n; for (int i = 0; i < n; i++) { cout << i; } return 0; } Decrease: #include <fstream> int main() { std::ifstream y("input.txt"); std::ofstream z("output.txt"); int n, i = 0; y >> n; while(i < n) z << i++; exit(0); } What's about "fstream"? std::fstream y("input.txt"), z("output.txt") It's amazing but output is not correct.) "output.txt" isn't remaking. Output is writing from begin of file. How to decrease code? Just for fun)

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Why I am getting Presentation Error [on hold]

- by user105697

Below is my code. When I submit it in UVA they are giving me Presentation error. I want to know the reason. I have tried all possible ways. In my code I use 2D-array to store each word of a sentence. I also want to know the reason for giving presentation error. #include<stdio.h> #include<string.h> int main() { char a[10000],ar[100][10000]; int i,j,k,m,n,l,len[10000],c; freopen("input.txt","r",stdin); while(gets(a)) { k=0; i=0; c=0; for(j=0; ; ++k) { if(a[k]==' ' || a[k]=='\0') { ar[i][j]='\0'; len[i]=c; if(a[k]=='\0') break; i++; j=0; c=0; } else { ar[i][j]=a[k]; c++; j++; } } for(m=0; m<=i; m++) { for(n=(len[m]-1); n>=0; n--) { printf("%c",ar[m][n]); } printf(" "); } printf("\n"); } return 0; }

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How to redirect output away from /dev/null

- by Gowtham

I have an application that runs the a command as below: <command> >& /dev/null I have no control on this. All the o/p generated by this command goes to /dev/null. I want the output to be visible on screen or redirected to a log file. I tried to use freopen() and related functions to reopen /dev/null to another file, but could not get it working. Do you have any other ideas? Is this possible at all? Thanks for your time. PS: I am working on Linux. -Gowtham

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How to catch printf from a dll?

- by Xarx

I've got a C++ console application that uses a third-party dll (jvm.dll, indirectly) that uses printf to print various error messages (Java stacktrace). I need to catch these stacktraces to a string in order to process them further, or at least to see them printed on the console. The thing is that I see the stacktrace only when debugging my application in VisualStudio (VS 2010). When I run my application in the "normal way", i.e. from the command line, nothing is printed on the console. So VS is able to somehow interfere the java output and display it. I need to be able to do the same thing. I've already tried freopen(), but without success. Also, I've found this question on the same problem, but without a clear answer.

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Internal "Tee" setup

- by RadlyEel

I have inherited some really old VC6.0 code that I am upgrading to VS2008 for building a 64-bit app. One required feature that was implemented long, long ago is overriding std::cout so its output goes simultaneously to a console window and to a file. The implementation depended on the then-current VC98 library implementation of ostream and, of course, is now irretrievably broken with VS2008. It would be reasonable to accumulate all the output until program termination time and then dump it to a file. I got part of the way home by using freopen(), setvbuf(), and ios::sync_with_stdio(), but to my dismay, the internal library does not treat its buffer as a ring buffer; instead when it flushes to the output device it restarts at the beginning, so every flush wipes out all my accumulated output. Converting to a more standard logging function is not desirable, as there are over 1600 usages of "std::cout << " scattered throughout almost 60 files. I have considered overriding ostream's operator<< function, but I'm not sure if that will cover me, since there are global operator<< functions that can't be overridden. (Or can they?) Any ideas on how to accomplish this?

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How to find minimum weight with maximum cost in 0-1 Knapsack algorithm?

- by Nitin9791

I am trying to solve a spoj problem Party Schedule the problem statement is- You just received another bill which you cannot pay because you lack the money. Unfortunately, this is not the first time to happen, and now you decide to investigate the cause of your constant monetary shortness. The reason is quite obvious: the lion's share of your money routinely disappears at the entrance of party localities. You make up your mind to solve the problem where it arises, namely at the parties themselves. You introduce a limit for your party budget and try to have the most possible fun with regard to this limit. You inquire beforehand about the entrance fee to each party and estimate how much fun you might have there. The list is readily compiled, but how do you actually pick the parties that give you the most fun and do not exceed your budget? Write a program which finds this optimal set of parties that offer the most fun. Keep in mind that your budget need not necessarily be reached exactly. Achieve the highest possible fun level, and do not spend more money than is absolutely necessary. Input The first line of the input specifies your party budget and the number n of parties. The following n lines contain two numbers each. The first number indicates the entrance fee of each party. Parties cost between 5 and 25 francs. The second number indicates the amount of fun of each party, given as an integer number ranging from 0 to 10. The budget will not exceed 500 and there will be at most 100 parties. All numbers are separated by a single space. There are many test cases. Input ends with 0 0. Output For each test case your program must output the sum of the entrance fees and the sum of all fun values of an optimal solution. Both numbers must be separated by a single space. Example Sample input: 50 10 12 3 15 8 16 9 16 6 10 2 21 9 18 4 12 4 17 8 18 9 50 10 13 8 19 10 16 8 12 9 10 2 12 8 13 5 15 5 11 7 16 2 0 0 Sample output: 49 26 48 32 now I know that it is an advance version of 0/1 knapsack problem where along with maximum cost we also have to find minimum weight that is less than a a given weight and have maximum cost. so I have used dp to solve this problem but still get a wrong awnser on submission while it is perfectly fine with given test cases. My code is typedef vector<int> vi; #define pb push_back #define FOR(i,n) for(int i=0;i<n;i++) int main() { //freopen("input.txt","r",stdin); while(1) { int W,n; cin>>W>>n; if(W==0 && n==0) break; int K[n+1][W+1]; vi val,wt; FOR(i,n) { int x,y; cin>>x>>y; wt.pb(x); val.pb(y); } FOR(i,n+1) { FOR(w,W+1) { if(i==0 || w==0) { K[i][w]=0; } else if (wt[i-1] <= w) { if(val[i-1] + K[i-1][w-wt[i-1]]>=K[i-1][w]) { K[i][w]=val[i-1] + K[i-1][w-wt[i-1]]; } else { K[i][w]=K[i-1][w]; } } else { K[i][w] = K[i-1][w]; } } } int a1=K[n][W],a2; for(int j=0;j<W;j++) { if(K[n][j]==a1) { a2=j; break; } } cout<<a2<<" "<<a1<<"\n"; } return 0; } Could anyone suggest what am I missing??

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