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I was working on a problem for Project Euler using C++ in Code::Blocks 10.05 and found my program to be crashing in a strange place: the initialization. Here is a code snippet that reproduces the problem.
#include <iostream>
#include <vector>
#include <deque>
using namespace std;
vector<deque<uint32_t> > f;
int main()
{
deque<uint32_t> p;
deque<uint32_t>::iterator dit1,dit2;
p.push_back(0);
p.push_back(1);
f.push_back(p);
cout << f.back().size() << endl;
cout << "f= ";
for(dit1==f.back().begin();dit1!=f.back().end();dit1++) cout << *dit1 << " ";
cout << "Checkpoint" << endl;
return 0;
}
Before posting here, I tried a test program to see if I could figure out the problem.
#include <iostream>
#include <deque>
#include <vector>
using namespace std;
int main(void)
{
uint64_t i;
deque<uint32_t> d;
vector<deque<uint32_t> > vd;
deque<uint32_t>::iterator it;
for(i=1;i<=5;i++) d.push_back(i);
vd.push_back(d);
for(it=vd.back().begin();it!=vd.back().end();it++) cout << *it << " ";
return 0;
}
The first program crashes while the second correctly reproduces the deque. Besides variable names, the only major difference I see is the first program uses a global variable and the test program uses a local variable. So why does the first program crash in the for loop while the second does not?
You used == instead of = in the for loop in the first program.
Related
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I have simplified the code to get rid of unrelated objects. This is my code:
#include <iostream>
#include <fstream>
using namespace std;
fstream asdf;
int input;
void import_image(){
asdf.seekg(0);
char character;
for(int k = 0; k < 40; k++){
asdf.get(character);
input = (unsigned int)(unsigned char)character;
}
}
void print_hello_world(){
for(int rows; rows <= 27; rows++){
cout << "hello world" << endl;
}
cout << "goodbye.";
}
int main(){
asdf.open("abc.txt", ios::binary | ios::in);
cout << asdf.is_open() << endl;
import_image();
//cout << endl;
print_hello_world();
return 0;
}
Running this code results only in
1
goodbye.
--------------------------------
Process exited after 0.1511 seconds with return value 0
however removing double slash (simply adding cout << endl;) fixes everything. I have no idea why it happens and would like to now why is it so. I know that variable "rows" has no value, but why does printing a new line fix everything?
The new "endl"
is a great sign
that what you see,
is called "UB".
Your program has Undefined Behavior (UB) because your int rows that you use for the loop iterations is uninitialized.
By UB definition anything may happen. Activate all (sane) compiler warnings to find errors like this earlier in your development process.
Undefined behavior yield working programs by completely random changes (for example the addition of std::endl) but in the end it's undefined behavior.
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I'm a student who just learned to use C++ for a few weeks. I write C++ code on Code:: Block and I am trying to run this code to learn about vector:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
vector<int> intVector;
for(int i = 0; i < 10; i++)
{
intVector.push_back(i+1);
}
cout << "Numbers in vector: ";
for(int i = 0; i < intVector.size(); i++)
{
cout << intVector[i] + " ";
}
}
But the output is really weird:
Numbers in vector: vector::_M_emplace_back_auxector::_M_emplace_back_auxctor::_M_emplace_back_auxtor::_M_emplace_back_auxor::_M_emplace_back_auxr::_M_emplace_back_aux::_M_emplace_back_aux:_M_emplace_back_aux_M_emplace_back_aux
Process returned 0 (0x0) execution time : 0.047 s
Press any key to continue.
Does anyone know how to fix this problem? Do I use vector in the wrong way?
Try changing the cout line like this:
cout << intVector[i] << " ";
What you're trying to do is add an int& and a string literal -- in some compilers it will emit a warning indicating for you that you're not getting what you intended for.
For example with Clang:
warning: adding '__gnu_cxx::__alloc_traits>::value_type' (aka 'int') to a string does not append to the string [-Wstring-plus-int]
cout << intVector[i] + " ";
~~~~~~~~~~~~~^~~~~
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What have I done wrong with the following code?
#include <iostream>
using namespace std;
main ()
{
int a;
int b;
int sum;
cout << "Enter first number \n";
cin >> a;
cout << "Enter second number \n";
cin >> b;
sum = a+b;
cout << "The sum of both numbers is" << sum << endl;
return 0;
}
Does the editor you are using tells errors, so the code is not executing? Or som exception rises? Or it is executing but nothing is shown? Please specify your problem accurately.
Anyway, you must use
int main ()
instead of
main()
Notice that your code returns a value. The last line of you code is:
return 0;
Thus, you must specify an int return type.
Check your initial lines with this.
#include <iostream>
using namespace std;
int main ()
{
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Whenever I try to run this program it returns an error saying:
no operator "<<" matches these operands
Also note that the program only runs into this problem in the getChoice() function.
#include <iostream>
#include "utilities.h"
using namespace std;
int getChoice(string inChoices[]){
int numOfChoices = sizeof(inChoices) / sizeof(inChoices[0]);
string x = inChoices[0];
string y = inChoices[1];
cout << x << endl << y << endl;
return numOfChoices;
}
int main()
{
string choices[2] = { "Happy Day", "Even Better Day" };
cout << utilities::getChoice(choices) << endl;
cout << endl << sizeof(choices) / sizeof(choices[0]) << endl;
}
You need also to include the string header:
#include <string>
You need to #include <string>
And your calculation of numOfChoices in getChoice() is wrong, since the parameter inChoices is actually a "pointer to string" instead of "array of strings".
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thanks for taking the time to help me out.
I'm really new with C++ and Xcode. I was working on a simple program to help me understand loops, so my goal was to make a simple "echo machine". This is my code:
string words;
int main()
{
do {
cout << "Enter text.";
cin >> words;
cout << "You entetered " << words << "!";
}
while (words != "goodbye");
return 0;
}
My result is nothing but lldb in parenthesis. I am very frustrated and can't find what I'm doing wrong anywhere. Please help and thank you so much.
Are you just missing the include directives for the standard headers you're using?
Try this:
#include <iostream>
#include <string>
using namespace std;
int main() {
string words;
do {
cout << "Enter text: ";
cin >> words;
cout << "You entered " << words << "!\n";
} while (words != "goodbye");
return 0;
}