`printf`¶

Defined in header <Kokkos_Printf.hpp>^{since Kokkos 4.2} which is included from <Kokkos_Core.hpp>

Usage¶

Kokkos::printf("Hello World!");
Kokkos::printf("Pi is approx %.2f\n", 3.14159);
Kokkos::printf("Value at index %d: %f\n", i, data[i]);

Prints formatted output to the standard output stream (stdout). This function can be called from both host and device code, including within parallel kernels. The behavior is analogous to std::printf, but returns void instead of an integer to ensure consistent behavior across backends.

Interface¶

template<typename ...Args> KOKKOS_FUNCTION void printf(const char *format, Args... args);¶

Added in version 4.2.

Parameters:

format – Null-terminated string specifying how to format the output, using format specifiers compatible with C printf
args – Values to be printed according to the format string

Returns:

void (unlike std::printf which returns the number of characters written)

Format Specifiers¶

Supports standard C printf format specifiers:

%d, %i - signed integer
%u - unsigned integer
%f - floating point
%e, %E - scientific notation
%g, %G - shortest representation
%s - string
%p - pointer
%x, %X - hexadecimal
Width, precision, and length modifiers (e.g., %.2f, %10d)

Example¶

Basic Usage¶

#include <Kokkos_Core.hpp>

int main(int argc, char* argv[]) {
    Kokkos::initialize(argc, argv);
    {
      Kokkos::printf("Starting computation\n");

      Kokkos::parallel_for("hello", 4, KOKKOS_LAMBDA(int i) {
          Kokkos::printf("hello world from thread %d\n", i);
      });
      Kokkos::fence();

      Kokkos::printf("Computation complete\n");
    }
    Kokkos::finalize();
}

Debugging Values¶

Kokkos::parallel_for("debug", n, KOKKOS_LAMBDA(int i) {
    if (i < 5) {  // Limit output for large arrays
        Kokkos::printf("data[%d] = %.6f\n", i, data(i));
    }
    if (data(i) < 0) {
        Kokkos::printf("Warning: negative value at index %d: %f\n", i, data(i));
    }
});

Notes¶

Warning

Calling printf() from a kernel may affect register usage and reduce performance. Use sparingly in performance-critical code.

printf¶

Usage¶

Interface¶

Format Specifiers¶

Example¶

Basic Usage¶

Debugging Values¶

Notes¶

See also¶

`printf`¶