Default values on arguments in C functions and function overloading in C

Question

Converting a C++ lib to ANSI C and it seems like though ANSI C doesn\'t support default values for function variables or am I mistaken? What I want is something like

Answer 1

No, Standard C does not support either. Why do you feel you need to convert your C++ code to C? That could get quite tricky - I'd have thought writing wrappers would be the way to go, if your C++ must be callable from C.

Answer 2

i think u can use a function with variable arguments here is my example

#include <stdarg.h>
#include <stdio.h>
void baz( int flag, ... )
{
    va_list ap;
    char *bar = "baz"; /* default value */
    va_start( ap, flag );
    if ( flag == 1 )
        bar = va_arg( ap, char * );
    va_end( ap );
    printf( "%s\n", bar );
}
int main( void )
{
    baz( 0 );
    baz( 1, "foo");
    baz( 2 );
    baz( 1, "bar");
    return 0;
}

the output is

baz
foo
baz
bar

if u look for example man 2 open they say

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>

       int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode);

       int creat(const char *pathname, mode_t mode);

       int openat(int dirfd, const char *pathname, int flags);
       int openat(int dirfd, const char *pathname, int flags, mode_t mode);

but mode is actually a ... argument

Answer 3

There is a way to support as many default parameters you need, just use a structure.

// Populate structure with var list and set any default values
struct FooVars {
  int int_Var1 = 1;  // One is the default value
  char char_Command[2] = {"+"};
  float float_Var2 = 10.5;
};
struct FooVars MainStruct;

//...
// Switch out any values needed, leave the rest alone
MainStruct.float_Var2 = 22.8;
Myfunc(MainStruct);  // Call the function which at this point will add 1 to 22.8.
//...

void Myfunc( struct FooVars *MyFoo ) {
  switch(MyFoo.char_Command) {
    case '+':
      printf("Result is %i %c %f.1 = %f\n" MyFoo.int_Var1, MyFoo.char_Command, MyFoo.float_Var2, (MyFoo.float_Var2 + MyFoo.int_Var1);
      break;
    case '*':
      // Insert multiply here, you get the point...
      break;
    case '//':
      // Insert divide here...
      break;
  }
}