Question

Q6 Common Mistakes in C

5 Points

Each of the following code samples below is making a common mistake in C. From the options:

probable segfault, double free, incorrect use of free, logic error, memory leak, and no error

select the error type that best categorizes the mistake.

You can assume all the code has the necessary #include macros. Also you should assume that the system is 32-bit.

1) #DEFINE PASSWORD "correct horse battery staple"
char *check_permissions (char *user_guess) {
     if (user_guess = PASSWORD) {
          return "access granted";
     }
     return "access denied";
}

#DEFINE PASSWORD "correct horse battery staple" char *check_permissions (char *user_guess) f if (user_guessPASSWORD) return "access granted" return "access denied";

2) #DEFINE PASSWORD "correct horse battery staple"
char *check_permissions (char *user_guess) {
     if (user_guess == PASSWORD) {
          return "access granted";
     }
     return "access denied";
}

3) int main () { char *x = malloc(0xFFFFFFFF * sizeof(char)); x[0] = '!'; }

4) int foo () { int *x = malloc(20); x[0] = x[1] = 1; x[2] = x[0] + x[1]; x[3] = 99; return x[3]; }

5) int main () {

  char *x = "patrick";
  printf("%s", x);
  free(x); // tidy up
}

Answer 1

1.) it is a logical error on line 3 if condition. In if it should be "==" not "=".

2.) It will give no error as all the calls and conditions are good without any error.

3.) Here seg fault will occur as 0xFFFFFFFF is representation of -1 and thus malloc will not assign any memory for it in char *x and on the next line during assignment will give a seg fault.

4.) Here there will be memory leak as not the exact amount that is needed by an int is allocated and after using the required space like 16 of 20 bytes the rest of 4 bytes may be leaked.

5.) incorrect use of free here as in main function the memory is freed by itself without using free() explicitly.

Please see the above screenshot. It is the 2nd program run on my side with its out put.

Int main () { double pitch [] = { 0, 523.3, 587.3, 659.3, 698 . 5, 784.0, 880.0, 932.3, 987.8 }�: int music [] = { 5, 3, 3, 0, 0, 0, 4, 2, 2, 0, 0, 0, 1, 2, 3, 4, 5, 5, 5, 0, 0, 0, 5, 3, 3, 0, 0, 0, 4, 2, 2, 0, 0, 0, 1, 3, 5, 5, 1 }�: for (int t = 0�: t < 39�: t + +) { if (music [t] = = 0) Sleep (150)�: else Beep (pitch [music [t]]