C++ :: Arrays Are Actually Created With A Size Indication?
Jan 14, 2014
Reading Effective C++ by Scott Meyers, and Item 16 claims that when an array is created, the compiler reserves a block of memory at the very beginning to indicate how many objects are in the array.
n = number of objects
|n|index0|index1|...etc
Scott Meyers wrote:This is just an example, of course. Compilers aren't required to implement things this way, though many do.
Supposedly, this how delete knows how many objects to destruct. And if you were to do something like:
int* foo = new int;
//Stuff
delete[] foo;
Then delete would interpret the first block as the number of items to destruct, then continue on and destruct that many blocks of memory onward, causing UD behavior.
I am having some problem with my quick sort problem. My program is supposed to create 5 arrays with 5,10,15,and 20 random integers, respectively. Then it should sort those arrays, where the numbers are bigger or smaller than the middle element in the original array! The program I wrote should do that but, its not! The program just keeps running infinitely!
#include <iostream> #include <cstdlib> using namespace std; void p(int k[],int left, int right) { int i = left, j = right;
Trying to do a homework assignment for a class and how to read a file into an array. I've looked in our book and on several other forums and cant seem to find any examples of this. Below is the assignment I'm working on. I have a shell of the program that I can get to run, but getting a .txt file to read into an array is something I cant seem to figure out how to do.
Write a program to read N data items into two arrays, X and Y, of size 20. Store the product of the corresponding pairs of elements of X and Y in a third array Z, also of size 20. Print a three column table that displays the arrays X, Y, and Z. Then compute and print the square root of the sum of the items in array Z. Compute and print the average of the values in array Z and print all values above the average of array Z. Determine the smallest value in each array using only one function.
Use the two data files named DATAX.TXT and DATAY.TXT.
You must use functions for the reading of the data, computing the average, printing the three column table and printing the values above average.
// Music Shuffle Program // This program takes an array of strings and randomly permutes their order. // This allows us to generate new song shuffles. #include <iostream>
how do I tell the if statement to output this error message 'exceeded the maximum amount of characters' that has its characters stored in an array using c-style string?
[INPUT] The cat caught the mouse! [OUTPUT] Exceeded the maximum amount of characters (max 10) #include<iostream> #include<string>
comparing with screen size the height is bigger but lenght is smaller. I don't understand.
I can understand that different printers process the fonts in different way and then to have different lenghts. That's not the problem. The problem is I need to simulate in screen the same behaviour i will have on printer because these texts are being aligned in the document, and I don't want to see that the text si aligned different in text than in paper.
What can I do to render the text on screen with the same size I will have on the printer? Print preview is doing it. Should I change the font parameters? is something related with pixels per inch?
I am developing a small game using MFC in which the game options like new game, save, open, exit etc. can be selected from the menu as well as from the buttons inside the window. I have no problems with the menu but the buttons do not seem to work at all.
The buttons are created at runtime using CButton class. To associate the buttons with the corresponding functions, I just used the same resource ID for the buttons as the menu options, but that did not work. When I click on the buttons, nothing happens. If I assign different resource IDs to the buttons, how do I handle the message map entries? Do I have to write different message map entries for the menus and the buttons while their function is exactly the same?
I'm currently creating a text-based RPG, to get myself back into learning C++ again. The problem seems to be with the if-else ladder of statements, the user selects which race they wish to play as, which as a result creates the appropriate object for that race.
This is the character selection option code:
std::cout << "Please select a race: Human [1], Elf [2], Dwarf [3] or Orc [4] "; std::cout << "Race selection: "; std::cin >> race_selection; std::cin.ignore(); switch (race_selection) {
[Code] .....
The problem here is, regardless of which race I use using the above switch statement, the Human object always seems to be created, instead of the object for the desired race.
make a class that you can make only one Object of it.
For example if you have Class A. Let's say you create one object A* a=new A();
Now the next time you, try to create another object. For example:
A* b=new A(); What will happen is that b will get the same object (or reference) as a. In other words hey'll be pointing towards the same place. So basically you'll only have one object of it created. I tried doing it but I couldn't quite make it.
Here is what I tried: (but couldn't complete the exercise)
class God { public: static int num; static God* god;
I have a combobox which doesn't have the CBS_SORT style and after adding some items I'd like to offer the ability for the user to sort it alphabetically by clicking on a given button. How can I sort the combobx after it has been created and some items added to it ?
I was wondering why, in C, the sizeof of a struct is larger than the the sum of all the sizeofs of it's members. It only seems to be by a few bytes, but as a bit of a perfectionist I fine this a bit annoying.
I am trying to pass a 2D array called f (coming from a text file with 9 columns of numbers and 297,680 rows) that was created using the vector container in my main() to the function myfunc. I'm just trying to figure out how to pass the address of f in main() to myfunc(), so that myfunc() has arguments consisting of a pointer g (that accepts the address of f as an input) and an int.
This is the error from the compiler: test_2d.cc: In function ‘int main()’: test_2d.cc:47:25: error: cannot convert ‘std::vector<std::vector<double> >*’ to ‘double (*)[297680][9]’ for argument ‘1’ to ‘int myfunc(double (*)[297680][9], int)’ return myfunc(&f,count); ^ Here is my code:
#include <iostream> #include <fstream> #include <iomanip> //allow setprecision to get all the decimal points #include <vector> #include <string>
does a pointer keep track of time stamps when it is created? i am trying to use it to create a table that can store the access count and the temporal locality at the same time.
im trying to get the row id created when inserting, ive tried ; SCOPE_IDENTITY(), get_last_identity() adding it to the end of my query string but get nothing back, it doesnt even add row to database. ive also tried adding a stored procedure but it doesnt even have the option in adding that when i right click to add it,(i thinks its because im using microsoft Access MySql)
so the program will create a random value for the inflow. The idea is that the internal for loop will continue to run until the fill_level of the reservoir, which starts at 0, hits the capacity. The process of simulating how many years (each iteration of the internal for loop representing a year) is to be repeated 10 times by the parent for loop of the water_level simulation for loop.
The problem is that the random number that is supposed to created are the same number. THey are different every time I run it, but they are the same every time the loops repeat to make a new simulation.
I discovered valgrind and started using it for my c code. But I get following error message at almost every malloc position, :
==19505== 40 errors in context 10 of 12: ==19505== Use of uninitialised value of size 8 ==19505== at 0x10000416E: my_method (main.c:662) ==19505== by 0x10000159E: main (main.c:182) ==19505== Uninitialised value was created by a heap allocation ==19505== at 0x47F1: malloc (vg_replace_malloc.c:302) ==19505== by 0x100001C21: my_method (main.c:333) ==19505== by 0x10000159E: main (main.c:182)
and I really don't understand what it means. I already googled it but I didn't find out what is my mistake.SO here i just put one example:
Code:
int main(int argc, char** argv) {
//i declare my variables at this position Uint *used, *forbidden_jumps, *forbidden_jumpsV, *forbidden_jump;
/*now i want to allocate one of them, this is my line 333 from the error message*/
//a_num is set during the execution of the program, ALLOC(used, Uint, a_num); }
[code].....
Is there any support page for the output of valgrind? I found it on the homepage.
I'm expected to get a starting minimum input, and also an ending maximum output (for example: 21, and 25). From here, i have to give output using all the numbers (in a row) between the min and max numbers.
(for the same example: 21 22 23 24 25)
I assumed I would want to create an array using a variable, but i'm not sure of that either.
I got everything in this code running except for my remove function. What the project does is adds or removes an integer to a chain of integers created by the user. My add function works the first time but after that if I try to remove or add I believe it is pointing to the improper location and I don't know how to fix this....
Here is my code:
Header: // adds "number" to the array pointed to by "arrayPtr" of "size". // Note the size of the array is thus increased. void addNumber(int *& arrayPtr, int number, int &size); // removes a "number" from the "arrayPtr" of "size". // if "number" is not there -- no action
