CSE 333 24su Exercise 2

Due: Wednesday, June 26th, 2024 by 10:00 am; No late exercises accepted.
Goals: Use pointers to access and print arbitrary memory bytes and addresses, and explore C data structure representation in memory.

Description: Your job is to write a C function that prints, in hex, the values of the bytes allocated to some variable. The function's prototype is

void PrintBytes(void* mem_addr, int num_bytes);

and its output looks like this:

The 4 bytes starting at 0x7fff1081856c are: ff 01 30 4e

You should use the following main function in the program you submit (you should be able to copy and paste this code from the assignment web page rather than having to re-type it):

int main(int argc, char **argv) {
  char     char_val = '0';
  int32_t  int_val = 1;
  float    float_val = 1.0;
  double   double_val  = 1.0;

  typedef struct {
    char     char_val;
    int32_t  int_val;
    float    float_val;
    double   double_val;
  } Ex2Struct;

  Ex2Struct struct_val = { '0', 1, 1.0, 1.0 };

  PrintBytes(&char_val, sizeof(char));
  PrintBytes(&int_val, sizeof(int32_t));
  PrintBytes(&float_val, sizeof(float));
  PrintBytes(&double_val, sizeof(double));
  PrintBytes(&struct_val, sizeof(struct_val));

  return EXIT_SUCCESS;
}

Your implementation of PrintBytes will need to do a few things:

• convince the compiler to let you access bytes in memory, given the address of the first byte to be printed as a void* pointer value.
• use a loop to iterate once for each byte in the variable, using a pointer to extract that byte and print it.
• figure out how to use format specifiers to printf in order to print out an uint8_t byte in lower-case hexadecimal, using exactly two digits. As a hint, take inspiration from this code:

  #include <inttypes.h>
  ...
    uint8_t a_byte = 0xD1;
    printf("The byte is: %02" PRIx8 " -- enjoy!\n", a_byte);
  ...

• figure out how to print a pointer value.

Your code should produce output that is identical to the following, except for values that might change from one execution to the next because of randomness outside of your control. That randomness includes variable addresses and the values of uninitialized data or padding bytes.

$bash gcc -Wall -std=c17 -g -o ex2 ex2.c
$bash ls
ex2 ex2.c
$bash ./ex2
The 1 bytes starting at 0x7fff3c84a1ff are: 30
The 4 bytes starting at 0x7fff3c84a1f4 are: 01 00 00 00
The 4 bytes starting at 0x7fff3c84a1f8 are: 00 00 80 3f
The 8 bytes starting at 0x7fff3c84a1e8 are: 00 00 00 00 00 00 f0 3f
The 24 bytes starting at 0x7fff3c84a1d0 are: 30 b0 f0 00 01 00 00 00 00 00 80 3f 00 00 00 00 00 00 00 00 00 00 f0 3f

(Note that the last output line is actually a single line, but probably wraps in your browser. Also, note that the number of bytes shown on the last line is not the sum of the number of bytes shown on the previous lines.)

You must not alter the given main function code. If you notice any style issues with it, ignore them and focus on getting your new code right.

---

As usual, your code must:

• Compile without errors or warnings on CSE Linux machines (lab workstations, attu, or CSE home VM) with gcc -Wall -g -std=c17 -o ex2 ex2.c -- do not submit a Makefile.
• Have no crashes, memory leaks, or memory errors on CSE linux machines. (Suggestion: valgrind)
• Follow the quality guidelines we covered in class, including the formatting, modularization, variable and function names, and so on. If in doubt, follow the Google C++ style guide. We also suggest using cpplint --clint.
• Be robust: you should think about handling bogus input from the user (if any), and you should handle hard-to-handle cases (if there are any) gracefully.
• Have a comment at the top of each source file with your name, and CSE or UW email address.

You should submit your exercise to the course Gradescope.