C++ Program crash when doing string assign

Question

I have a weird problem, this is my code :

test.h

#ifndef _test_
#define _test_
#include <iostream>
#include <string>
class Test {
public:
    Test();
    ~Test();
    void addName(std::string _Name);
private:
    std::string Name;
};
#endif // _test_

test.cpp

#include "test.h"
Test::Test() {}
Test::~Test() {}
void Test::addName(std::string _Name) {
    std::cout << _Name << std::endl;
    Name = _Name;
    std::cout << _Name << std::endl;
}

main.cpp

#include "test.h"
int main(int argc, char* argv[]) {
    Test* project;
    project->addName("abc");
    return 0;
}

Results :

abc

The program has unexpectedly finished.

Why are you declaring project as a pointer? I suggest you get rid of it being a pointer and the code should work fine after changing -> to .. — NathanOliver
– NathanOliver, Commented Jul 18, 2016 at 14:01
Totally unrelated to your problem, but don't use leading underscore followed by an upper-case letter, such symbols are reserved in all scopes. — Some programmer dude
– Some programmer dude, Commented Jul 18, 2016 at 14:04

Some programmer dude · Accepted Answer · 2016-07-18 14:02:18Z

6

That's because you have a pointer to a Test object, but it doesn't actually point anywhere. That leads to undefined behavior when you try to dereference the pointer.

Declare the object as an actual object, not a pointer:

Test project;
project.addName("abc");

answered Jul 18, 2016 at 14:02

Some programmer dude

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Comments

MikeCAT · Accepted Answer · 2016-07-18 14:02:45Z

1

The pointer project is default-initialized and has indeterminate value, so dereferencing it has a big chance to cause abnromal termination of the program.

Try creating an object and assigning it before dereferencing like this:

#include "test.h"
int main(int argc, char* argv[]) {
    Test* project = new Test;
    project->addName("abc");
    delete project;
    return 0;
}

edited Jul 18, 2016 at 14:02

answered Jul 18, 2016 at 14:02

MikeCAT

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3 Comments

crashmstr Over a year ago

No reason to use new here.

johnbakers Over a year ago

@crashmstr there is a need to use new here if the OP wishes to use *project. Otherwise, there is no reason to use new here if the OP changes what project is.

MikeCAT Over a year ago

@johnbakers *project can be used without new like this: Test hoge; Test *project = &hoge;

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