Hi guys, given the following code: int shmid= shmget(key, SIZE, 0666); char *addr= shmat(shmid, 0, SHM_W); // Optional code here; shmdet((const void *) addr); Should I use free(addr) after detaching my shared memory from the current addres space?

Hi guys, given the following code: int shmid= shmget(key, SIZE, 0666); char *addr= shmat(shmid, 0, SHM_W); // Optional code here; shmdet((const void *) addr); Should I use free(addr) after detaching my shared memory from the current addres space?

No. Shmdt detaches the shared memory from your address space which is good enough. However you can still reattach the shared memory to your process's address space later. If you don't want to reattach it, you should call shmctl. You don't have to call free.

thank you very much!

thank you very much!

basic rule: malloc/free should match

/get cbook

/get

hello every one i want to ask someone who has an experience in js i find it difficult . how can i learn it pls

i mean i want the good way to learn it

First if all you shouldn't even touch JS, that thing is cursed. Secondly, I am sorry but this is a C/C++ board.

What's swap? You are returning float by value. So function is float addition (){}

After all same?

After all same?

No syntax is also incorrect

*confused nick young. Isn't when reading input is inputting into string ? Just iterate the string and check the ASCII value

I'm sorry but I've been learning this for exactly two days. In assembler numbers are perceived separately like I see 999 and I just need to go through this as a line and it will find these three nines ???

Is there anyone here who is good at math?

Yeah

Is there anyone here who is good at math?

Literally studied my entire life

Is there anyone here who is good at math?

dontasktoask.com

Does someone know boost asio at good level? I have a couple of questions.

dontasktoask.com

Does someone know boost asio at good level? I have a couple of questions.

idem

dontasktoask.com

you must be getting tired of sharing the same link xd

you must be getting tired of sharing the same link xd

You can't imagine, people do not even read the http://www.catb.org/esr/faqs/smart-questions.html in the rules

https://cdecl.org/

You can't imagine, people do not even read the http://www.catb.org/esr/faqs/smart-questions.html in the rules

I mean reading is kinda boring sometimes ngl.

I mean reading is kinda boring sometimes ngl.

Yes, just like the non-questions that it answers

Yes, just like the non-questions that it answers

Yeah, I wish we could read each other's mind, that wouldn't cause any problems

Yeah, I wish we could read each other's mind, that wouldn't cause any problems

Well GUESS WHAT, we have a tool for that called language that people have spent the last centuries pulling appart to prove that it can express anything with only mild levels of ambiguity

Well GUESS WHAT, we have a tool for that called language that people have spent the last centuries pulling appart to prove that it can express anything with only mild levels of ambiguity

eh, fair enough, can't argue with that

eh, fair enough, can't argue with that

Don't try or I'll need to quote 5 dozen linguists and take psychic damage for it

Hi i need help Need a solution to the exercise?

Hi, I had a look at it, I see you don't have the previous issue reproducible, but running valgrind showed me another one in derivative_Chebyshev_T, you have new and delete for an array, but there's a possible return in-between that may resulting in not calling that delete and memory leak. Looking at this part of code and other parts it seems that you not really using RAII, which is one of the most important features of C++. You can use gsl::finally, or write one yourself to call arbitrary cleanup code on scope end. Or if it's available to you, use std::vector, (with optimizations and exceptions disabled it doesn't have a lot of overhead), or if you're not sure you can just write a class that allocates memory in constructor, deallocates in desctuctor and has all copy/move deleted (or implemented, but then be careful with the implementations, e.g. your matrix implementation allocated in move constructor, which probably a lot of runtime overhead if you don't care about the moved-from object).

Yes, sorry, I didn't put a compatible input file in the repo for testing. Thanks for derivative_Chebyshev_T I didn't notice. I don't know what it RAII, I guess I'll read about it on cppreference.com or if you have a better source it'll be welcomed. I can't use the STL because once the code is complete I plan to translate it to CUDA and CUDA (at least the version I can use) doesn't support STL. About the move operator in Matrix2D I allocate one element of T with the default constructor so that the object on the other side gets something allocated so that its constructor doesn't try to deallocate something that wasn't allocated. I'm not sure if that's the best way to do it. Thanks a lot for your time and answers

hi, i would like to know which algorithm std::sort uses... i was reading this and it mentions time complexity, but it doesn't seem to tell which algorithm it is https://en.cppreference.com/w/cpp/algorithm/sort

I'm sorry but I've been learning this for exactly two days. In assembler numbers are perceived separately like I see 999 and I just need to go through this as a line and it will find these three nines ???

What OS and arch exactly that you learn?

hi, i would like to know which algorithm std::sort uses... i was reading this and it mentions time complexity, but it doesn't seem to tell which algorithm it is https://en.cppreference.com/w/cpp/algorithm/sort

This varies from implementation to implementation. The libstdc++ provided by GNU uses introsort. Libc++ provided by Clang uses mergesort initially and then when the number of elements in the smaller arrays are less than a specified value, it reverts to insertion sort. https://en.m.wikipedia.org/wiki/Introsort

Yes, sorry, I didn't put a compatible input file in the repo for testing. Thanks for derivative_Chebyshev_T I didn't notice. I don't know what it RAII, I guess I'll read about it on cppreference.com or if you have a better source it'll be welcomed. I can't use the STL because once the code is complete I plan to translate it to CUDA and CUDA (at least the version I can use) doesn't support STL. About the move operator in Matrix2D I allocate one element of T with the default constructor so that the object on the other side gets something allocated so that its constructor doesn't try to deallocate something that wasn't allocated. I'm not sure if that's the best way to do it. Thanks a lot for your time and answers

You don't have to do a dummy allocation. You can set the pointer to nullptr. Deleting a null pointer is perfectly alright. In your move constructor just set other.arr to nullptr after moving its resources.

You don't have to do a dummy allocation. You can set the pointer to nullptr. Deleting a null pointer is perfectly alright. In your move constructor just set other.arr to nullptr after moving its resources.

True, thanks

☹️

Yes, sorry, I didn't put a compatible input file in the repo for testing. Thanks for derivative_Chebyshev_T I didn't notice. I don't know what it RAII, I guess I'll read about it on cppreference.com or if you have a better source it'll be welcomed. I can't use the STL because once the code is complete I plan to translate it to CUDA and CUDA (at least the version I can use) doesn't support STL. About the move operator in Matrix2D I allocate one element of T with the default constructor so that the object on the other side gets something allocated so that its constructor doesn't try to deallocate something that wasn't allocated. I'm not sure if that's the best way to do it. Thanks a lot for your time and answers

I think cppreference explains it well, and by the way, your array class actually using this conception already (so I was not right saying that you're not using it), you just need to use it in more places instead of doing manual new[]

I think cppreference explains it well, and by the way, your array class actually using this conception already (so I was not right saying that you're not using it), you just need to use it in more places instead of doing manual new[]

I'm using new[]/delete[] in some functions because I was getting a warning: ISO C++ forbids variable length array

When I say: double array [n]; is this being allocated on the heap the same way new[] would?

In my case I can replace all the new[]/delete[] with objects of the Array I made

Mmm I may be mistaken (I'm a beginner), but from what I understood, in this way you know at compile time the dimension of the array, and if it's not too enormous it should be on the stack. Things are allocated on the heap when you do something like double *array; Because you don't know the dimension. But, again, I may be mistaken, so wait for someone more expert than me

I surely wrote some wrong things, if you could please correct me it would be useful for me, too

Mmm I may be mistaken (I'm a beginner), but from what I understood, in this way you know at compile time the dimension of the array, and if it's not too enormous it should be on the stack. Things are allocated on the heap when you do something like double *array; Because you don't know the dimension. But, again, I may be mistaken, so wait for someone more expert than me

That's what I think too.

Oh, so maybe I did understand something in class 😂

But I don't know how big the stack can be. In competitive programming it's common to see things like this: int MAXN = 1000; int G[MAXN][MAXN]; // do your stuff with the graph I guess such a big array needs to be allocated on the heap.

What OS and arch exactly that you learn?

Windows NASM x64 and x86

I'm using new[]/delete[] in some functions because I was getting a warning: ISO C++ forbids variable length array

You don't need variable size arrays (the ones that are not supported (VLA)), allocation on heap is OK, but just it usually good to hide it inside a class like std::vector or your Array class, not to forget to delete the array in all the places where it needed.

But I don't know how big the stack can be. In competitive programming it's common to see things like this: int MAXN = 1000; int G[MAXN][MAXN]; // do your stuff with the graph I guess such a big array needs to be allocated on the heap.

Some CP peoples logic are good but their knowledge about programming aren't not

They common use nonsense unportable code like #include <bits/stdc++.h .

I wonder if they learn with -pedantic-errors enabled, because you will never know what os and arch used to test the code, so it's best to stick with standard

They common use nonsense unportable code like #include <bits/stdc++.h .

best library ever

Windows NASM x64 and x86

https://stackoverflow.com/questions/8021772/assembly-language-how-to-do-modulo Actually i don't understand what you're talking about :<.

If it's reading from stdin and store it into string, just iterate until you find 0. and compare it one by one with ASCII value

Hello everyone

hi, i would like to know which algorithm std::sort uses... i was reading this and it mentions time complexity, but it doesn't seem to tell which algorithm it is https://en.cppreference.com/w/cpp/algorithm/sort

It generally uses a hybrid quicksort for large spans and for smaller spans within it a heap sort or insertion sort

Can I declare a binary arithmetic operator for a class that allows to multiply float to my class without using friend function? So myClass * someFloat and someFloat * myClass both will work

Can I declare a binary arithmetic operator for a class that allows to multiply float to my class without using friend function? So myClass * someFloat and someFloat * myClass both will work

Ok, seems I can't, but in my case I can make it just a normal free function. Context: friend doesn't work together with [[nodiscard]], and clang complains about their combination

, , ,

#include <iostream> using namespace std; int c; void & referance (){ return c; } int main(){ reference ()=20; cout<<"c ="<<c<<endl; return 0; }

#include <iostream> using namespace std; int c; void & referance (){ return c; } int main(){ reference ()=20; cout<<"c ="<<c<<endl; return 0; }

Can we say that is a return by reference code?

# include <iostream> # include <math.h> using namespace std; /* Determine the armstrong nunber: 512= pow((5+1+2),3); */ int armstrong (int n) { int r,result=0; while (n>0) { r=n/10; result=result+pow(r+r+r,3); n=n/10; } return result; } int main () { int n; cout<<"n="; cin>>n ; if(n==armstrong(n)){ cout<<"this nunber is an armstrong number"; } else{ cout<<"this nunber is not an armstrong number"; } return 0; }

# include <iostream> # include <math.h> using namespace std; /* Determine the armstrong nunber: 512= pow((5+1+2),3); */ int armstrong (int n) { int r,result=0; while (n>0) { r=n/10; result=result+pow(r+r+r,3); n=n/10; } return result; } int main () { int n; cout<<"n="; cin>>n ; if(n==armstrong(n)){ cout<<"this nunber is an armstrong number"; } else{ cout<<"this nunber is not an armstrong number"; } return 0; }

See if this error works

Can I use arthematic operator with if statements ?

Can I use arthematic operator with if statements ?

I don't use

#define BACKLOG 5 class TcpServer{ public: TcpServer(int port) : _port(port), _sock_listen(-1) {} ~TcpServer(){ } public: bool InitTcpServer(){ _sock_listen = socket(AF_INET, SOCK_STREAM, 0); if (_sock_listen < 0){ std::cerr << "socket error!" << std::endl; return false; } struct sockaddr_in local; memset(&local, 0, sizeof(local)); local.sin_family = AF_INET; local.sin_port = htons(_port); local.sin_addr.s_addr = INADDR_ANY; if (bind(_sock_listen, (struct sockaddr*)&local, sizeof(local) < 0)){ std::cerr << "bind error" << std::endl; return false; } if (listen(_sock_listen, BACKLOG) < 0) { std::cerr << "listen error" << std::endl; return false; } return true; } void Loop(){ while (true){ struct sockaddr_in peer; socklen_t len = sizeof(peer); int sock = accept(_sock_listen, (struct sockaddr*)&peer, &len); if (sock < 0){ std::cerr << "accept error" << std::endl; continue; } std::cout << "get a new link : " << sock << std::endl; } } private: int _port; int _sock_listen; };

i want to know why can't accept successful

The function "Loop" can't work, just all time to run "accept error"

Hi i need help Need a solution to the exercise?

dm me

If it's reading from stdin and store it into string, just iterate until you find 0. and compare it one by one with ASCII value

Thank you very much you very help

Can we say that is a return by reference code?

?

Are there any drawbacks of including headers that are already added to precompiled headers file? I guess only preprocessing time will be affected that should be not really noticeable?

Are there any drawbacks of including headers that are already added to precompiled headers file? I guess only preprocessing time will be affected that should be not really noticeable?

Errors maybe? Duplication hence compilation time.And why should you when you know this?

Errors maybe? Duplication hence compilation time.And why should you when you know this?

Some tools like clang analyser assume headers are compilable by themselves (which usually should be true if there are no precompiled headers)

So to use them I need to include all the headers needed (or forward declare the used types)

Some tools like clang analyser assume headers are compilable by themselves (which usually should be true if there are no precompiled headers)

The compilers differ in their mechanism which i dont wana dwell in now.You have used gcc

hi , looking for help with strtok_s function on c, any 1 can help?

Hello

#include <iostream> #include <conio.h> #include <math.h> #include <iomanip> using namespace std;   const float PI=3.14159265358979323 const float n=0.2032; float area(float dia) { return PI*dia*dia/4; } Int main() {             float pipel[2][4],piped[2][4],pipeqass[2][4],vel[2][4],hf[2][4],hfbyq[2] [4] ,delq[2][4],delq1,d elq2,qdash[2][4],sighf[2]={0,0},sighfbyq[2]={0,0};             int common[2][4];             float qpn,dp4,cpn;             for(int i=0;i<10;++i)             {                         cout<<"\nENTER THE VALUES OF PIPE IN LOOP"<<i+1;                          for(int j=0;j<10;++j)                          {                                      cout<<"\nPIPE NO"<<j+1;                                      cout<<"\nPIPE LENGTH(in m):";                                      cin>>pipel[i][j];                                      cout<<"\nPIPE DIAMETER(in mm):";                                      cin>>piped[i][j];                                      cout<<"\nIS IT A COMMON PIPE?(1-YES,0-NO)";                                      cin>>common[i][j];                                      cout<<"\nFIRST ASSUMED VALUE OF Q(in m^3/min)";                                      cin>>pipeqass[i][j];                          vel[i][j]=(pipeqass[i][j]/60)/area(piped[i][j]/1000);                          qpn=pow(pipeqass[i][j]/60,n);                                      if(pipeqass[i][j]>=0)                                      {                                      dp4=pow(piped[i][j]/1000,4.87);                                                  cpn=pow(100,n);                                      hf[i][j]=10.622*(pipel[i][j])*(qpn)/(cpn*dp4);                                      hfbyq[i][j]=hf[i][j]/pipeqass[i][j];                                                  if(i==0)                                                  {                                                              sighf[0]+=hf[i][j];                                                      sighfbyq[0]+=hfbyq[i][j];                                                  }                                                  if(i==1)                                                  {                                                              sighf[1]+=hf[i][j];                                                      sighfbyq[1]+=hfbyq[i][j];                                                  }                                      }                                      else                                      {                                                  dp4=pow(-piped[i][j]/1000,4.87);                                                  cpn=pow(100,n);                                      hf[i][j]=10.622*(pipel[i][j])*(qpn)/(cpn*dp4);                                      hfbyq[i][j]=hf[i][j]/pipeqass[i][j];                                                  if(i==0)                                                  { sighf[0]+=hf[i][j]; sighfbyq[0]+=hfbyq[i][j]; } if(i==1) { sighf[1]+=hf[i][j]; sighfbyq[1]+=hfbyq[i][j]; } } } delq1=-sighf[0]/(n*sighfbyq[0]); delq2=-sighf[1]/(n*sighfbyq[1]); } for(int i=0;i<10;++i) { for(int j=0;j<4;++j) { if(i==0) delq[i][j]=delq1; if(i==1)delq[i][j]=delq2; } } for(int i=0;i<10;++i) {for(int j=0;j<4;++j) { if(common[i][j]) { if(i==0) delq[i][j]=delq1-delq2; if(i==1) delq[i][j]=delq2-delq1; } } } for(int i=0;i<10;++i) { for(int j=0;j<4;++j) { qdash[i][j]=pipeqass[i][j]+delq[i][j]; } } cout<<"\n\n\nITERATION 1\n\n"; cout<<"SNO LEN(m) DIA(mm) C ASSQ(m^3/min) ASSQ(m^3/s) VEL(m/s) Hf(m) Hf/Q(m/m^3/min) delq(m^3/min) qdash(m^3/min)"; for(int i=0;i<10;++i) { cout<<"\n"; for(int j=0;j<4;++j) { cout<<i+1<<" "<<pipel[i][j]<<" "<<piped[i][j]<<" "<<100< <" "; std::cout<<std::setprecision(4)<<pipeqass[i][j]<<" "<<pipeqass[i][j]/60<<" "<<vel[i][j]<<" "<<hf[i][j]<<" "<<hfbyq[i][j]<<" "<<delq[i][j ]<<" "<<qdash[i][j]; } } getch();  return 0; }

Who can help correct the code in C++

Very urgent

Very urgent

Saying that won't give you any faster response specially in communities. We're not paid. It's most likely only going to add some ignorance, therefore only delaying responses.