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@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@ This is cppad-20221105 documentation. Here is a link to its current documentation .
Printing During Forward Mode: Example and Test

Running
To build this program and run its correctness test see cmake_check .

Source Code 
# include <cppad/cppad.hpp>

namespace {
    using std::cout;
    using std::endl;
    using CppAD::AD;

    // use of PrintFor to check for invalid function arguments
    AD<double> check_log(const AD<double>& y)
    {   // check during recording
        if( y <= 0. )
            cout << "check_log: y = " << y << " is <= 0" << endl;

        // check during zero order forward calculation
        PrintFor(y, "check_log: y == ", y , " which is <= 0\n");

        return log(y);
    }
}

void print_for(void)
{   using CppAD::PrintFor;

    // independent variable vector
    size_t n = 1;
    CPPAD_TESTVECTOR(AD<double>) ax(n);
    ax[0] = 1.;
    Independent(ax);

    // print a VecAD<double>::reference object that is a parameter
    CppAD::VecAD<double> av(1);
    AD<double> Zero(0);
    av[Zero] = 0.;
    PrintFor("v[0] = ", av[Zero]);

    // Print a newline to separate this from previous output,
    // then print an AD<double> object that is a variable.
    PrintFor("\nv[0] + x[0] = ", av[0] + ax[0]);

    // A conditional print that will not generate output when x[0] = 2.
    PrintFor(ax[0], "\n  2. + x[0] = ",   2. + ax[0], "\n");

    // A conditional print that will generate output when x[0] = 2.
    PrintFor(ax[0] - 2., "\n  3. + x[0] = ",   3. + ax[0], "\n");

    // A log evaluations that will result in an error message when x[0] = 2.
    AD<double> var     = 2. - ax[0];
    AD<double> log_var = check_log(var);

    // dependent variable vector
    size_t m = 2;
    CPPAD_TESTVECTOR(AD<double>) ay(m);
    ay[0] = av[Zero] + ax[0];

    // define f: x -> y and stop tape recording
    CppAD::ADFun<double> f(ax, ay);

    // zero order forward with x[0] = 2
    CPPAD_TESTVECTOR(double) x(n);
    x[0] = 2.;

    cout << "v[0] = 0" << endl;
    cout << "v[0] + x[0] = 2" << endl;
    cout << "  3. + x[0] = 5" << endl;
    cout << "check_log: y == 0 which is <= 0" << endl;
    // ./makefile.am expects "Test passes" at beginning of next output line
    cout << "Test passes if four lines above repeat below:" << endl;
    f.Forward(0, x);

    return;
}
int main(void)
{   print_for();

    return 0;
}

Output
Executing the program above generates the following output: 
 
    v[0] = 0
    v[0] + x[0] = 2
    Test passes if two lines above repeat below:
    v[0] = 0
    v[0] + x[0] = 2
Input File: example/print_for/print_for.cpp