cprintf.jl

function process_types(fmt :: String, args...)
  # Process types of arguments for libc's printf family.

  # Grab everybody's type.
  types = [typeof(arg) for arg in args]

  # Perform the following conversions:
  # string -> Ptr{Uint8} (for %s)
  # arrays -> Ptr{Void}  (for %p)
  types = map(t -> (t == ASCIIString ? Ptr{Uint8} : t), types)
  types = map(t -> (issubtype(t, Base.Array) ? Ptr{Void} : t), types)
  types = append!([Ptr{Uint8}], types)

  # ccall absolutely wants a tuple as 3rd argument.
  # A variable that evaluates to a tuple just won't do.
  typexpr = Expr(:tuple, types...)
  return typexpr
end

function c_printf(fmt :: String, args...)
  typexpr = process_types(fmt, args...)
  # Ignore printf's return value (an int).
  @eval ccall((:printf, "libc"), Void, $(typexpr), $(fmt), $(args...))
end

output.txt

   macro      eval      libc
1.43e-04  4.68e-02  2.09e-03

time_printf.jl

# Time some stuff.
include("cprintf.jl")

fmt = "%5d %s %8.1e %6.4f\n";
args = (12, "blablabla", pi/e, sqrt(2));
N = 1000;

# 1. @printf.
@printf("%5d %s %8.1e %6.4f\n", 12, "blablabla", pi/e, sqrt(2))
@printf("%5d %s %8.1e %6.4f\n", 12, "blablabla", pi/e, sqrt(2))
@printf("%5d %s %8.1e %6.4f\n", 12, "blablabla", pi/e, sqrt(2))
t = time();
for k = 1 : N
  @printf("%5d %s %8.1e %6.4f\n", 12, "blablabla", pi/e, sqrt(2))
end;
t_printf = (time()-t)/N;

# 2. print_formatted.
print_formatted(fmt, args...) = @eval @printf($fmt, $(args...))

print_formatted(fmt, args...)
print_formatted(fmt, args...)
print_formatted(fmt, args...)
t = time();
for k = 1 : N
  print_formatted(fmt, args...)
end;
t_print_formatted = (time()-t)/N;

# 3. c_printf.
c_printf(fmt, args...)
c_printf(fmt, args...)
c_printf(fmt, args...)
t = time();
for k = 1 : N
  c_printf(fmt, args...)
end;
t_c_printf = (time()-t)/N;

print_formatted("%8s  %8s  %8s\n", "macro", "eval", "libc")
print_formatted("%8.2e  %8.2e  %8.2e\n", t_printf, t_print_formatted, t_c_printf);