No output while doing try catch in c++

Question

I am trying to catch bad allocation error. When input length will be in order of 10000000000000000000000 or something, then bad allocation error should come. I don't know why its not being caught. Any help will be appreciated!

# include <vector>
# include <iostream>


using namespace std;

void length(int m)
{
    vector<int> x;

    try
    {
    x.resize(m);
    }
    catch(std::bad_alloc&) 
    {
        cout << "caught bad alloc exception" << std::endl;
    }
}

int main()

{

    int l;
    cout << "Length" ;
    cin >> l ;
    length(l);

    return 0;
}

UPDATED:

When I am hard coding the value for input, then it is throwing an exception. I don't know why its working this way.

# include <vector>
# include <iostream>


using namespace std;



void length(int m)
{
    vector<int> x;

    try
    {
    x.resize(m);
    }
    catch(std::bad_alloc&) 
    {
        cout << "caught bad alloc exception" << std::endl;
    }
}

int main()

{

    int m= 100000000000000000000;
    length(m);

    return 0;
}

I see the caught exception [running here](http://cpp.sh/9fwg) with a large input (e.g. 10000000000) — Cory Kramer, Apr 11 '17 at 14:19
Can it be a compiler issue? Because I am not getting this exception. — Surabhi Choudhary, Apr 11 '17 at 14:21
Just FYI on maximum size: [Related: Is there a max array length limit in C++?](http://stackoverflow.com/a/216266/1030110) — m0nhawk, Apr 11 '17 at 14:25
Note that `std::size_t` has a maximum value. If you try to request a vector with more than that number of elements, you will not actually be trying to allocate that many elements. — François Andrieux, Apr 11 '17 at 14:28
[Related](http://stackoverflow.com/questions/864416/are-some-allocators-lazy)? — François Andrieux, Apr 11 '17 at 14:28
[Pro tip] When you think it is right but it is not, outputting the variable to check what the program received is a useful debugging tool. — NathanOliver, Apr 11 '17 at 14:32
@jennifer Why not hard-code the value you claim should throw an exception, instead of the input hiding behind a `cin` statement? Then everyone will see what value you are trying instead of guessing. — PaulMcKenzie, Apr 11 '17 at 14:35

Bathsheba · Answer 1 · 2017-04-11T14:29:25.813

1

You ought to write

if (!(cin >> l)){
    // I could not read that into `l`
}

The lack of an exception being caught could be down to

Your int value being smaller than you think (perhaps some undefined wrap-around behaviour), and an exception is not thrown since the allocation is successful.
The allocation being lazy in the sense that the memory is not allocated until you actually use it.
If std::bad_alloc is thrown as an anonymous temporary then it will not be caught at your catch site. (Unless your naughty compiler allows non-const references to bind to anonymous temporaries, which some do as an extension). Write catch (const std::bad_alloc&) instead, and it will be caught there.

edited Apr 11 '17 at 14:29

answered Apr 11 '17 at 14:23

Bathsheba

231,907
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While correct in terms of how to capture the application should terminate with an uncaught exception if the exception was not caught. That is not happening so no exception is being thrown. – NathanOliver Apr 11 '17 at 14:24
Well this *proves* that `std::bad_alloc` is *not* being thrown. – Bathsheba Apr 11 '17 at 14:26
Indeed, but the OP has an `int` for `l`. – Bathsheba Apr 11 '17 at 14:33

score 0 · Answer 2 · answered Apr 11 '17 at 14:22

0

The maximum length of an integer type int is 2.147.483.647 . Are you sure you have actually used an higher number to test it?

answered Apr 11 '17 at 14:22

BotMaster3000

472
4
16

1

The maximum size of an `int` is undefined. All we know for sure is that it must be at least 32767. – NathanOliver Apr 11 '17 at 14:33
@NathanOliver: Prefer "implementation defined" to "undefined"? – Bathsheba Apr 11 '17 at 14:45
@Bathsheba Yes. I misspoke there. It is implementation defined. – NathanOliver Apr 11 '17 at 14:46

score 0 · Answer 3 · answered Apr 11 '17 at 14:41

You're passing Integer variable which has the limit. Minimum value for a variable of type short: –32768 Maximum value for a variable of type short: 32767
The error which you will get from your code is std::length_error
To raise the bad allocation error dynamically you can try malloc() with incorrect size OR try below code.

#include <iostream>
#include <new>

int main()
{
    try {
        while (true) {
            new int[100000000ul];
        }
    } catch (const std::bad_alloc& e) {
        std::cout << "Allocation failed: " << e.what() << '\n';
    }
}
</i>

Actually it's -32767, for a `short` *and* an `int`. Don't forget 1's complement and signed magnitude. — Bathsheba, Apr 11 '17 at 14:44

score 0 · Answer 4 · answered Apr 11 '17 at 15:15

No exception is thrown because the int that makes it through to your function void length(int m) is capped at its max value that is much less than vector::max_size(). Consider:

void length(int m)
{
    cout << "m is: " << m << " which has a max value: " << numeric_limits<int>::max() <<  endl;
    // ...
}

with the output: Length10000000000000000000000 m is: 2147483647 and has a max value: 2147483647

No output while doing try catch in c++

4 Answers4