I was trying out programs based on extern and as i understand, this is useful when accessing variables across multiple files having only one definition. But i tried a simple program as below without "extern" and thing seem to work when i expected it would fail during linking process
As i have included "var.h" in all header files without extern, "int a" would be included in both the .c file and during linking, compiler should have thrown a warning or error message but it compiles file without any issue. Shouldn't var.h have the following "extern int a"?
I am writing a piece of code that requires me to display the last 1000 lines from a multiple text files (log files). FYI, I am running on Linux and using g++.
I have a log file from which - if it contains more than 1000 lines, I need to display the last 1000 lines. However, the log file could get rotated. So, in case where the current log file contains less than 1000 lines, I have to go to older log file and display the remaining. For e.g., if log got rotated and new log file contains 20 lines, I have to display the 980 lines from old log file + 20 from current log files.
What is the best way to do this? Even an outline algorithm will work.
I'm using multiple C++ files in one project for the first time. Both have need to include a protected (#ifndef) header file. However, when I do that, I get a multiple definition error.
From what I found from research, adding the word inline before the function fixes the error. Is this the right way to do this, and why does it work? Should I make a habbit of just declaring any function that might be used in two .cpp files as inline?
I used to use map to access elements. map has a good feature that it sort the element automatically. Now I need a map which can access element through multiple key values. So I choosed boost::multi_index_container. I defined a container as follows.
struct elem { int a,b; elem(int aa,int bb):a(aa),b(bb) {} };
typedef multi_index_container <
[Code] ....
What I am wondering is whether boost::multi_index_container can sort elements automatically. Specifically, are all elements extracted through iterator from begin to end shown below having b values between 2 and 100?
test t; test::iterator begin = t.lower_bound(make_tuple(1,2)); test::iterator end = t.upper_bound(make_tuple(1,100));
am trying to create a program that asks the user personal questions.
std::vector<std::string> name, age, favsinger; std::cout << "Hello, what is your Name Age Favorite_Singer? "; std::cin << name; //i want to store the user's info along with the sibling's
I'm having a bit of trouble with something. What I'm trying to do is create a new Access table by combining other already existing Tables.
For instance, let's consider Table1 (with columns A, B and C), Table2 (with columns A, D and E) and Table3 (with columns A, F and G), where Table1.A = Table2.A = Table3.A.
From these, I want to create a new table TableResult, with columns A, B, C, D, E, F and G, with all the data contained in them. There's one catch: I want the code to get the names of the other columns, apart from column A.
I've thought about using Union, but I need to actually create a new table by combining the previous tables.
I've created a class called Voter with a private member variable ID, also I have a variable in my main function to be ID as well. I'm trying to compare the two ID's but when I do so:
if (ID == V.ID)
I get the error - 'std::string Voter::ID' is private within this context.
I know that because it's private I can't access it, but how do I?
I have two cpp files.I m updating a value of an integer in one cpp file and i want to perform a specific function in the second file as per to the value updated in the first file. ie I m initialing the variable in the constructor. I have two buttons in the first cpp file. On clicking the first button I m updating the variable as 1 and on pressing button two , I m updating the variable as 2. I m retrieving this variable in the second cpp file with respect to the object created for the class in the first cpp file.
The problem is that i m not able tot retrieve the updated value in the second file. only the initialized value is being retrieved. neither 1 nor 2 is updated.
So I have a rather large (for me) project, requiring me to have two .cpp files and a header. Anyway, both of the .cpp files #include the header file, but I recieve linker errors because the variables and functions in the header are declared and defined twice (once in each .cpp file). How am I supposed to do this?
We typically don't bother with massive, monolithic code files that get processed from top to bottom. In the Object Oriented world, code files don't mean much. In fact, in C#, I could have multiple classes defined in one file, or have one class split across several files.
I am struggling with the concept of having different ccp's and header files. I made a really bad example project for representation, but basically my question is are any of the #includes unnecessary that I have? Technically it functions, but if I am doing it wrong I want to prevent myself from starting bad habits in the future. My code just basically uses strings and sets a name and prints it. My code is really bad, but I wanted to just use includes in such a way for a quick example.
//MAIN.CCP #include "functions.h" using namespace std; int main()
I have a big un-editable program, A, which I need to run for like a 1000 different input files. It takes about 15 minutes for each file, so a little parallelisation wouldn't hurt.
I have installed openmpi and it works fine. I have made a small program, B, which selects an input file, moves it to another directory, calls program A with the path to the selected input file and then - when A is done - selects a new input file etc. It should loop until there are no more files in the initial directory.
The problem is this: When I have several processors they might pick the same file and that leads to errors. I have a working program, but it is not pretty.
Code:
#include <stdio.h> #include <mpi.h> #include <dirent.h> #include <string.h> #include <stdlib.h> int main(int argc, char *argv[]) { int num_procs, procs_id, i, exit; struct dirent *ent;
[Code]...
Every time a processor tries to move a file that another processor has just moved, the output shows an error message before looping to the next file and trying again. It works, but it is a bit annoying. So my questions are:
So say I create a header file which contains a list of structs, and I want to use these structs through out my source and some of my classes... how would I accomplish this?
When I try to do it via #include, I get re-definition errors, due to the nature of #pragma once. If I switch to #ifndef then I lack defenitions in files other than the source.
Is there a way to define things such as structs across multiple files, which doesn't lead to re-definition errors, and doesn't involve manually re-created all the structs for each file?
I am currently working on a C++ program for school. I am actually not finding too much difficulty in constructing the functions, enum-types, arrays and structs, however, I am finding great difficulty in using on ifstream variable to open multiple files.
I have posted the entire code that I have so far (even though I have pinpointed the issue to not properly opening the second file in ifstream).
I spent a couple of hours getting rid of certain functions/procedures, loops and variables and I get the same output (if what I removed doesnt crash it). I also get the same output whether I "open" the second file or not (meaning I removed all of the code for it and got the same output).
Here is the code (it's not finished because I am stuck on this file issue). It's a bit messy since I am now in debug mode versus program mode:
I have been working on code for quite some time and am able to successfully read in a text document and take certain words and information that I need. The issue is that I need to read in close to 100 plus documents and was wondering how I could read in the multiple documents. I thought about creating a structure of arrays and have each text document be an element and walk through taking each document but I am not sure how this works.
I am trying to get variables that are global to multiple files. I have mananged to make constant variables that are global but maybe not in the best way. In the header i have the constant variables being defined:
const int variable_Name = 5;
And the cpp file:
#include <iostream> using namespace std; #include "vars.h" int main ( ) { cout << variable_Name<< endl; system ("pause"); return 0; }
Is there a better way to do this and to make the variables able to be changed within the cpp files.
I am trying to create n number of files (n being an integer), by passing the name through a character array (and obviously changing its value at each iteration). But the problem is that the program compiles and executes but not a single file is created.
Here is my code snippet.
void file_phipsi(int m) { int a=0,n=0; char *str1;
I am new to c++ programming i just want to know how to write the data into different files.Suppose my input files has 1-8 ids so each id data must be stored into each different file. And below is my code.
