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Asked: 2026-05-13T13:34:53+00:00

I have the following code : #include <cstdarg> #include <iostream> using namespace std; class

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I have the following code :

#include <cstdarg>
#include <iostream>

using namespace std;

class a {
};

void fun1(a& aa, ...)
{
    va_list argp;
    va_start(argp, aa);
    char *p = 0;
    while ((p = va_arg(argp, char *)) != 0) {
        cout << p << endl;
    }
    va_end(argp);
}

void fun2(char *aa, ...)
{
    va_list argp;
    va_start(argp, aa);
    char *p = 0;
    while ((p = va_arg(argp, char *)) != 0) {
        cout << p << endl;
    }
    va_end(argp);
}

int main()
{
    cout << "fun2" << endl;
    fun2("a", "1", "2", (char *)0);
    cout << "fun1" << endl;
    fun1(a(), "1", "2", (char *)0);
    getchar();
}

Everything works fine with fun2. However, fun1 will just crash.

May I know how can I prevent from crashing, at the same time able to use class reference as 1st parameter.

Currently, it prints :

fun2
1
2
fun1

then crash.

I wish

fun2
1
2
fun1
1
2
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1 Answer

  1. Editorial Team

    You can’t use a reference parameter as the last named parameter with va_start. The reason is because va_start takes the address of the named parameter to find the location of the rest of the arguments. However, taking the address of a reference gives the address of the variable pointed at by the reference, not the address of the parameter itself. Your options are:

    1) change the variable type from a reference to a pointer (or a non-reference if you are OK with a copy of the passed in variable).

    2) Add an additional required parameter so that the reference isn’t the last named parameter. The additional parameter can be a useful parameter, such as one of the char* you are going to pass to your particular function, or it can be a dummy variable you just ignore.

    3) Change the definition of va_start. It’s not recommended, but you can do it. See http://support.microsoft.com/kb/119394 for a non-portable redefinition.

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