DevHeads IoT Integration Server•6mo ago

Are there any specific considerations for MSVC to avoid unexpected truncation during such conversion

I have a simple program with a getDouble() function returning a double value slightly above INT_MAX (2147483647). The program attempts to convert this value to an unsigned int using both direct and indirect casting. When compiling and running this code on MSVC x86, the direct cast truncates the double value to 2147483648 that's one more than INT_MAX. This is unexpected because the value should fit within the range of an unsigned int typically 32-bits on x86. Funny enough, this behavior is not observed on GCC which is another compiler. I've checked the Microsoft documentation but haven't found a specific explanation for this truncation on x86. Is this a known behavior of MSVC x86 for double to unsigned int conversions, especially when the double value is slightly above INT_MAX?

2 Replies

Marvee Amasi•6mo ago

Here is the code from the editor :

#include <stdio.h>

double getDouble() {
  double value = 2147483649.0;
  return value;
}

int main() {
  unsigned int directCast;
  double d;

  printf("INT_MAX: %u\n", INT_MAX);
  printf("UINT_MAX: %u\n", UINT_MAX);

  printf("Double value: %f\n", getDouble());

  directCast = (unsigned int)getDouble();
  printf("Direct cast value: %u\n", directCast);

  d = getDouble();
  printf("Indirect cast value: %u\n", (unsigned int)d);

  return 0;
}

#include <stdio.h>

double getDouble() {
  double value = 2147483649.0;
  return value;
}

int main() {
  unsigned int directCast;
  double d;

  printf("INT_MAX: %u\n", INT_MAX);
  printf("UINT_MAX: %u\n", UINT_MAX);

  printf("Double value: %f\n", getDouble());

  directCast = (unsigned int)getDouble();
  printf("Direct cast value: %u\n", directCast);

  d = getDouble();
  printf("Indirect cast value: %u\n", (unsigned int)d);

  return 0;
}

Marvee Amasi•6mo ago

Are there any specific considerations for MSVC to avoid unexpected truncation during such conversions? @Middleware & OS

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Are there any specific considerations for MSVC to avoid unexpected truncation during such conversion