CODEWITHSUNDEEP
c++variadic-functions
Paty Banana
Paty Banana

Reputation: 13

Function is getting only the first variadic argument value right

This function should pretty obviously return the minimum float value, but it always returns 0. While debugging, I found out that the va_arg() function gets only that 31 right, then it gets some strange numbers, one of them every time being 0.

float var_min(int, float, ...);

void main()
{
    cout << var_min(7, 31, 12, 4.5, 9, 22, 69, 8.21);
}

float var_min(int z, float, ...)
{
    int i = 0;
    float min, p;
    va_list ap;
    va_start(ap, z);
    min = va_arg(ap, float);
    for (i = 1; i < z; i++)
    {
        p = va_arg(ap, float);
        min = (min < p) ? min : p;
    }
    va_end(ap);
    return min;
}

Edit: this is the assignment:

Determine the minimum of a 10 float numbers from a string (implicit values or from the KB) using a function with a variable number of parameters. The first 7 values will be considered initially, next the last 3 and at the end these 2 values.

Upvotes: 0

Views: 245

Answers (1)

Eric Postpischil
Eric Postpischil

Reputation: 223643

To use va_arg starting with the second argument, change:

float var_min(int z, float, ...)

to:

float var_min(int z, ...)

(If there will always be at least one floating-point argument after z, and you wish to include it in the parameter list, then give it a name, initialize min from it directly, and change va_start(ap, z) to use its name instead of z.)

To pass float or double arguments to a variable-argument function, they must be explicitly of float or double type; integer types will not be converted to floating-point types, so:

var_min(7, 31, 12, 4.5, 9, 22, 69, 8.21);

should be:

var_min(7, 31., 12., 4.5, 9., 22., 69., 8.21);

In variable arguments, float arguments are promoted to double, so va_arg(ap, float) should be va_arg(ap, double) in both places it appears, and float min, p; should be double min, p;.

void main() is not a standard declaration for main. It could be int main().

Upvotes: 1

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