Defined int parameter[NUM] returned segment fault

[victor wang]

Hi all,
I'm having an issue with defining "int parameter[num]".
It success when compiling the code.
But If I run my application, it will show segment fault error to me when defining int parameter[num].

if(DBG)
    {
        qDebug("DIDO_Light_on function in!");
    }
    int result[DI_num];       
    if(DBG)
    {
        qDebug("result function defined!");
    }
    int err_flag = false;
    QString get;
    //QStringList result;
    QStringList DI_get_value;
    QStringList DO_set_value_low;
    QStringList DO_set_value_high;

It crashes at int result[DI_num];

What did I miss?

[sierdzio]

Please paste the code: your variable definition and exactly the line where it crashes.

[victor wang]

@sierdzio
Thanks for reminding.
I have modified the question just now.

[J.Hilk]

@victor-wang
are you sure DI_num is a positive value? If not than that's undefined behavior.

[victor wang]

@J.Hilk
Yes, I'm sure it is a positive value.
I defined it in mainwindow.h like below.

private:

    int Comport_Count,LED_Light,PingIP_1,PingIP_2,a,b,height,width,can1_rec_prt,can0_send_prt,burn_chk,Burn_count,a_cpu,b_cpu,LanTabClick,DidoTabClick,dido_count;
    int count,active_test_item,test_result_count;
    int DI_num,DO_num,showconnectcount;

[sierdzio]

And it compiles? In C++ arrays cannot have dynamic sizes, what's between [ and ] should be a constant expression.

[victor wang]

@sierdzio
I'm using arm-poky-linux-gnueabi-g++

So I can only use static parameter between [ and ]?

[J.Hilk]

@victor-wang
yes, since C99 I believe.

if you want a dynamically sized array, you should use QVector<int>

---

yes, since C99 I believe. nope, had that wrong, variable length arrays are a C99 feature only.
But C++ standard (till C++11) doesn’t support variable sized arrays. The C++11 standard mentions array size as a constant-expression.
However the GCC compiler seems to provide an extension to support them.

[Devopia53]

Not standard but latest gcc/g++ available. But first initialized. like this:

int DI_num{1024}, ...;

or

DI_num = 1024;
int result[DI_num];

[victor wang]

@J.Hilk
I would try to use QVector later

[victor wang]

@Devopia53
But DI_num would get a dynamic parameter form ini file.
I will convert String to int and give it to DI_num.

So I should defined it like int DI_num{1024}; first then give the new parameter to DI_num?

[Devopia53]

@victor-wang

This is possible if the value of the variable is set to an appropriate value before the array declaration is executed. But, I recommend using a vector.