how can i know the allocated memory size of pointer variable in c [duplicate]

Answer 1

There is no portable way but for windows:

#include 
#include 

#if defined( _MSC_VER ) || defined( __int64 ) /* for VisualC++ or MinGW/gcc */    
#define howmanybytes(ptr) ((unsigned long)_msize(ptr))
#else
#error no known way
#endif

int main()
{
  char *x=malloc(1234);

  printf( "%lu", howmanybytes(x) );

  return 0;
}