C Programming: Review Questions

Memory and Strings

In the example below, which variables are guaranteed to print the value of zero?

int a;
static int b;

void func() {
   static int c;
   int d;
   printf("%d %d %d %d\n",a,b,c,d);
}

In the example below, which variables are guaranteed to print the value of zero?

void func() {
   int* ptr1 = malloc( sizeof(int) );
   int* ptr2 = realloc(NULL, sizeof(int) );
   int* ptr3 = calloc( 1, sizeof(int) );
   int* ptr4 = calloc( sizeof(int) , 1);
   
   printf("%d %d %d %d\n",*ptr1,*ptr2,*ptr3,*ptr);
}

Explain the error in the following attempt to copy a string.

char* copy(char*src) {
 char*result = malloc( strlen(src) ); 
 strcpy(result, src); 
 return result;
}

Why does the following attempt to copy a string sometimes work and sometimes fail?

char* copy(char*src) {
 char*result = malloc( strlen(src) +1 ); 
 strcat(result, src); 
 return result;
}

Explain the two errors in the following code that attempts to copy a string.

char* copy(char*src) {
 char result[sizeof(src)]; 
 strcpy(result, src); 
 return result;
}

Which of the following is legal?

char a[] = "Hello"; strcpy("World", a);
char b[] = "Hello"; strcpy("World12345", b);
char* c = "Hello"; strcpy("World", c);

Complete the function pointer typedef to declare a pointer to a function that takes a void* argument and returns a void*. Name your type 'pthread_callback'

typedef ______________________;

In addition to the function arguments what else is stored on a thread's stack?

Printing

Spot the error!

fprintf(stdout, "You scored 100%");

Formatting - printing to a file

Complete the following code to print to a file. Print the name, a comma and the score to the file 'result.txt'

char* name = .....;
int score = ......
FILE *f = fopen("result.txt",_____);
if(f) {
    _____
}
fclose(f);

Formatting - printing to a string

How would you print the values of variables a,mesg,val and ptr to a string? Print a as an integer, mesg as C string, val as a double val and ptr as a hexadecimal pointer. You may assume the mesg points to a short C string(<50 characters). Bonus: How would you make this code more robust or able to cope with?

char* toString(int a, char*mesg, double val, void* ptr) {
   char* result = malloc( strlen(mesg) + 50);
    _____
   return result;
}

## Input. Parsing
Why should you check the return value of sscanf and scanf?

Why is 'gets' dangerous?

Write a complete program that uses `getline`

## Heap memory
When would you use calloc not malloc? 
When would realloc be useful?