C Programming, Review Questions

Topics

• C Strings representation
• C Strings as pointers
• char p[]vs char* p
• Simple C string functions (strcmp, strcat, strcpy)
• sizeof char
• sizeof x vs x*
• Heap memory lifetime
• Calls to heap allocation
• Deferencing pointers
• Address-of operator
• Pointer arithmetic
• String duplication
• String truncation
• double-free error
• String literals
• Print formatting.
• memory out of bounds errors
• static memory
• fileio POSIX vs. C library
• C io fprintf and printf
• POSIX file IO (read, write, open)
• Buffering of stdout

Questions/Exercises

• What does the following print out

int main(){
    fprintf(stderr, "Hello ");
    fprintf(stdout, "It's a small ");
    fprintf(stderr, "World\n");
    fprintf(stdout, "place\n");
    return 0;
}

• What are the differences between the following two declarations? What does sizeof return for one of them?

char str1[] = "another";
char *str2 = "another one";

• What is a string in c?
• Code up a simple my_strcmp. How about my_strcat, my_strcpy, or my_strdup? Bonus: Code the functions while only going through the strings once.
• What should the following usually return?

int *ptr;
sizeof(ptr);
sizeof(*ptr);

• What is malloc? How is it different than calloc. Once memory is malloced how can I use realloc?
• What is the & operator? How about *?
• Pointer Arithmetic. Assume the following addresses. What are the following shifts?

char** ptr = malloc(10); //0x100
ptr[0] = malloc(20); //0x200
ptr[1] = malloc(20); //0x300

 * `ptr + 2`
 * `ptr + 4`
 * `ptr[0] + 4`
 * `ptr[1] + 2000`
 * `*((int)(ptr + 1)) + 3`

• How do we prevent double free errors?
• What is the printf specifier to print a string, int, or char?
• Is the following code valid? If so, why? Where is output located?

char *foo(int var){
    static char output[20];
    snprintf(output, 20, "%d", var);
    return output;
}

• Write a function that accepts a string and opens that file prints out the file 40 bytes at a time but every other print reverses the string (try using POSIX API for this).
• What are some differences between the POSIX filedescriptor model and C's FILE* (ie what function calls are used and which is buffered)? Does POSIX use C's FILE* internally or vice versa?

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