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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 .
Print During Zero Order Forward Mode: Example and Test
# include <cppad/cppad.hpp>

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

    // use of PrintFor to check for invalid function arguments
    AD<double> check_log(const AD<double>& u, std::ostream& s_out)
    {   // check AD<double> value during recording
        if( u <= 0 )
            s_out << "check_log: u = " << u << " which is <= 0\n";

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

        return log(u);
    }
}

bool print_for(void)
{   bool ok = true;
    using CppAD::PrintFor;
    std::stringstream stream_out;
    double eps99 = 99.0 * std::numeric_limits<double>::epsilon();

    // independent variable vector
    size_t np = 1;
    size_t nx = 1;
    size_t ny = 1;
    CPPAD_TESTVECTOR(AD<double>) ap(np), ax(nx), ay(ny);
    ap[0] = 1.0;
    ax[0] = 2.0;
    Independent(ax, ap);
    //
    // define f(x, p) = log(p) + log(x)
    ay[0] = check_log(ap[0], stream_out) + check_log(ax[0], stream_out);
    CppAD::ADFun<double> f(ax, ay);
    //
    // zero order forward
    // both x and p are positive so no output generated
    CPPAD_TESTVECTOR(double) p(np), x(nx), y(ny);
    p[0] = 1.0;
    x[0] = 2.0;
    f.new_dynamic(p);
    f.check_for_nan(false);
    y = f.Forward(0, x, stream_out);
    ok &= stream_out.str() == "";
    ok &= CppAD::NearEqual(y[0], std::log(p[0]) + std::log(x[0]), eps99, eps99);
    //
    // zero order forward
    // p is negative so output generated
    p[0] = -1.0;
    x[0] = 2.0;
    f.new_dynamic(p);
    f.check_for_nan(false);
    y = f.Forward(0, x, stream_out);
    ok &= stream_out.str() == "check_log: u = -1 which is <= 0\n";
    ok &= std::isnan(y[0]);
    //
    return ok;
}
Input File: example/general/print_for.cpp