What is the problem in this code ? It shows memory dump error in runtime
#include<iostream>
using namespace std ;
int main()
{
int A[3][4] = {{3, 1, 8, 11}, {4, 12, 9, 10}, {7, 5, 2, 6}};
int **p = A;
P[1][2] = 99;
cout<<A[1][2] ;
}
Change your int **p = A[0][0] to int *p = &A[0][0]. In the next line, write the following *p = *((int*)p + 1 * NUM_OF_COLUMNS + 2) = 99;, where NUM_OF_COLUMNS is the number 4, instead of the P[1][2] = 99;. Correct the spelling of main as well as uppercase/lowercase of variables. Also add a return 0; at the end since you have an int main() and not a void.
you seem new to c++ or programming with a question like this one don't feel bad because pointers can be tricky and if you don't know you don't know. I am pretty sure this will help you. Remember to pick the best answer :).
#include <iostream>
using namespace std;
int main() {
int A[3][4] = { { 3, 1, 8, 11 }, { 4, 12, 9, 10 }, { 7, 5, 2, 6 } };
cout << "Before pointer change A[1][2] = " << A[1][2] << endl;
int *p; //Set pointer
p = &A[1][2]; //Set memory address to pointer don't forget '&'
*p = 99; //Change integer
cout << "After pointer change A[1][2] = " << A[1][2] << endl;
return 0; // you need a 'return 0;' because your main is int
}
Related
I am using gcc compiler on ubuntu 16 , when I am printing value garbage value is getting displayed
#include <bits/stdc++.h>
int Arrayprint(int r, int l, unsigned int* q)
{
r = 3;
l = 4;
for (int i = 0; i < r; i++) {
for (int j = 0; j < l; j++) {
cout << *(q + sizeof(unsigned int) * (i * l + j)); //Garbage getting diplay
cout << *(q + i + j); //this working
cout << "\t";
}
}
cout << "size of unsigned int : " << sizeof(unsigned int); //4
cout << "size of int : " << sizeof(int); //4
}
int main()
{
unsigned int image[R][L] = { { 1, 2, 3, 4 },
{ 5, 6, 7, 8 },
{ 9, 10, 11, 12 } };
unsigned int* q = (unsigned int*)image;
Arrayprint(R, L, q);
}
From what I can tell, you understand at a low level that the address of the ith element of an array of T is base + sizeof(T) * i. That's correct, and it's good that you know that.
However, C and C++ handle this for you already. When you say q + i or q[i], it's actually compiling that into q + sizeof(T)*i anyway (with the latter also dereferencing the result).
So when you say q[sizeof(int)*i], that's actually compiling into *(q + sizeof(int)*sizeof(int)*i), which is clearly not what you wanted.
Thus, the index in the array you actually access is off by a factor of sizeof(int) and results in an out of bounds error, which is where your strange numbers are coming from.
I am using gcc compiler on ubuntu 16 , when I am printing value
garbage value is getting displayed
Instead of trying to fix what's broken in your raw array arimethics, consider using the standard containers:
#include <iostream>
#include <array>
constexpr size_t R = 3;
constexpr size_t L = 4;
using image_t = std::array<std::array<unsigned int, L>, R>;
void Arrayprint(const image_t& q) {
// range based for loops for convenience
for(auto& row : q) { // get references to each row
for(unsigned int colval : row) { // get the column values
std::cout << colval << "\t"; // print the values
}
std::cout << "\n";
}
}
int main() {
image_t image = {{{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}};
Arrayprint(image);
}
Output:
1 2 3 4
5 6 7 8
9 10 11 12
I would like to convert an array of Integers
2, 3, 4, 8
5, 7, 9, 12
1, 0, 6, 10
to a string with the entries of that matrix appended in clockwise order
“2, 3, 4, 8, 12, 10, 6, 0, 1, 5, 7, 9”.
I have to keep declaration of int * Matrix and char * OutBuffer the way they are
int main()
{
int matrixArray[rowCount][columnCount] =
{ {2, 3, 4, 8},
{5, 7, 9, 12},
{1, 0, 6, 10}};
int * matrix;
string prebuffer;
char * outBuffer;
outBuffer = new (nothrow) char[24];
matrix = &matrixArray[0][0];
BuildStringFromMatrix(matrix, rowCount, columnCount, outBuffer);
}
I declare and address all my pointers before passing them in. However, I am not sure if I am going about allocating memory for the outBuffer to store the characters of prebuffer correctly?
void BuildStringFromMatrix(int* Matrix, int NumRows, int NumColumns, char * OutBuffer)
{
string prebuffer;
bool stringLeft = true;
int i = 0;
while (stringLeft)
{
int clockwiseDir[12] = { 1,1,1,4,1,1,0,4,-4,-1,-1,-1 };
prebuffer = to_string(Matrix[i]) + ", ";
OutBuffer = new char [prebuffer.length() + 1];
cout << prebuffer;
i += clockwiseDir[i];
if (i == 6)
{
prebuffer = to_string(Matrix[i]) + " ";
cout << prebuffer;
stringLeft = false;
}
}
}
**When I do not implement OutBuffer I have no trouble accessing and printing the matrix in clockwise format
But I how would I go about using OutBuffer to reference and print prebuffers contents??
I need numbers to display not unprintable symbols on the ASCII table
Thanks in advance :)
**
Firstly, in your loop under BuildStringFromMatrix function you are not using your i value anywhere.
Second, matrix = matrixArray should do fine.
I have a struct that has hardcoded data in it, however I can't figure out how to get c++ to display the data. What I am trying is:
#include <iostream>
using namespace std;
const int MAX = 8;
struct test {
int x[MAX] = { 16, 21, 308, 45, 51, 63, 17, 38 };
float y[MAX] = { 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5 };
int z[MAX] = { 8, 7, 6, 5, 4, 3, 2, 1 };
} id[MAX] = { 1, 2, 3, 4, 5, 6, 7, 8 };
int main() {
for (int counter = 0; counter < MAX; counter++) {
cout << id[counter].x << ", " << id[counter].y << ", "<< id[counter].z << endl;
}
}
I suggest you change your data layout:
struct Triplet
{
int x;
float y;
int z;
};
Next, make a container of the values:
std::vector<Triplet> test;
Or
Triple test[MAXIMUM_CAPACITY];
This should make your initializations easier.
It may also speed up your program by keeping relevant data closer together in the data cache.
I can't figure out how to get c++ to display the data.
You've been shooting over regarding usage of hardcoded arrays.
You don't need to double up your dimensions for struct. Any struct initialization will preserve the necessary memory for it's members.
You probably meant to write something like
#include <iostream>
using namespace std;
const int MAX = 8;
struct test
{
int x; // A simple int
float y; // A simple float
int z; // A simple int
} const id[MAX] = // Preserve the dimension. Note the const, to prevent changing the
// hardcoded values.
// Initialize the triples as needed
{ { 16, 1.5, 8 } ,
{ 308, 2.5, 7 } ,
// Place more triples here ...
{ 38, 8.5, 1 }
};
int main()
{
for (int counter = 0; counter < MAX; counter++)
{
cout << id[counter].x << ", " << id[counter].y << ", "<< id[counter].z << endl;
}
return 0;
}
See the Live Demo
The idiomatic c++ way to write this would be
struct test {
int x; // A simple int
float y; // A simple float
int z; // A simple int
};
std::array<test,MAX> id {{
{ 16, 1.5, 8 } ,
{ 308, 2.5, 7 } ,
// Place more triples here ...
{ 38, 8.5, 1 }
}};
See Live Demo
This question already has answers here:
Now that we have std::array what uses are left for C-style arrays?
(7 answers)
Closed 8 years ago.
array<int, 5> b = {12,45,12,4};
int B[5] = { 12, 45, 12, 4 };
for (auto item : b)
{
cout << item << endl; // 12,45,12,4, 0
}
cout << endl;
for (auto item : B)
{
cout << item << endl; // 12,45,12,4, 0
}
What is the difference between array<int,5> b; and int b[5];?
Template class std:;array is defined as a structure. It is an aggregate and has some methods as for example size().
The difference is for example that arrays have no assignment operator. You may not write
int b[5] = { 12, 45, 12, 4 };
int a[5];
a = b;
while structures have an implicitly defined assignment operator.
std::array<int, 5> b = { 12, 45, 12, 4 };
std::array<int, 5> a;
a = b;
Also using arrays you may not use initialization lists to assign an array. For example the compiler will issue an error for the following statement
int b[5];
b = { 12, 45, 12, 4, 0 };
However you can do these manipulations with std::array For example
std::array<int, 5> b;
b = { 12, 45, 12, 4, 0 };
This is my example:
#include "stdafx.h"
#include <iostream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
int ar[][3] = {1, 2, 3, 4, 5, 6, 7};
//cout << int[3]<<endl; // error C2062: type 'int' unexpected.
cout << "sizeof(ar) / sizeof(int[3]) "<< sizeof(ar) / sizeof(int[3]) << endl;;
system("pause");
return 0;
}
It is from a book, though no explanation was given. What is int[3] here and why it works only as an argument of sizeof in this case?
int[3] is a type declaration that represents an array of three integers.
Your commented code gives an error because you can't use a type as a variable.
sizeof(int[3]) is the size, in bytes, of an array of three integers. sizeof isn't an actual function that gets called while your program is running - it is resolved at compile time. sizeof(ar) / sizeof(int[3]) will give you the number of rows in your array, since each row is 3 integers long (you declared it as int ar[][3]).
The declaration
int ar[][3] = {1, 2, 3, 4, 5, 6, 7};
is for an array of triplets of integers - it is a 2D array.
The sizeof expression
cout << "sizeof(ar) / sizeof(int[3]) "<< sizeof(ar) / sizeof(int[3]) << endl;
prints the number of full triplets that you get. The last integer, 7, will not fall into any triplet. You should see 2 printed. ar[0] will contain {1, 2, 3} and ar[1] will contain {4, 5, 6}.