A3 - debugging and standard IO

common bugs

• syntax and compilation errors: caught by compilers before running
• logical errors
• memory management errors
• off-by-one errors
• using uninitialized variables

standard IO

• standard IO streams:

  • standard input (stdin): keyboard command line input
  • standard output (stdout): command line output
  • standard error (stderr): special error stream

• format specifier help the compiler know what data type is being used:

standard output

• found in <stdio.h>, eg: printf, putchar, fflush, stdout

• C stores IO in temporary memory called buffer:

  • line buffering: transmitted as a block when a new-line character is added
  • full buffering: transmitted as a block when a buffer is filled
  • no buffering: transmitted as they are written

• printf is line buffered

• it will not be printed until a new line is added, ie. /n

• fflush(stdout) prints the output buffer

• to change the buffering mode of stdout to unbuffered: setvbuf(stdout, NULL, _IONBF, 0) \\_IONBF = no buffering

• to reset it: setvbuf(stdout, NULL, _IOLBF, 0) \\_IOLBF = line buffering

standard input

• found in <stdio.h>, eg: scanf, 'getchar', 'fgets', stdin

#include <stdio.h>
#include <string.h>

#define BUFFER_SIZE 1000

int main() {
    char name[50];
    char buffer[BUFFER_SIZE];
    int age;
    char c;

    printf("enter your name: ");
    scanf("%49s", name); // Limit input to avoid buffer overflow
    printf("enter your age: ");
    scanf("%d", &age); // takes a reference to the age variable
    printf("your name is %s and you are %d years old.\n", name, age);

    // scanf can leave a newline character in the input buffer
    // clear the input buffer before using fgets
    while ((c = getchar()) != '\n' && c != EOF);

    printf("enter a character: ");
    c = getchar(); // reads a single character
    printf("you entered: %c\n", c);

    // printf("enter a line of text (gets - unsafe): ");
    // gets(buffer); // unsafe, can cause buffer overflow
    // printf("you entered: %s\n", buffer);

    printf("enter a line of text (fgets - safe): ");
    fgets(buffer, BUFFER_SIZE, stdin); // safely reads up to BUFFER_SIZE - 1 characters
    printf("you entered: %s\n", buffer);

    while ((c = getchar()) != '\n' && c != EOF); // clear the input buffer again

    while (fgets(buffer, BUFFER_SIZE, stdin) != NULL) {
        if (strcmp(buffer, "exit\n") == 0) {
            break; // exit the loop if the user types "exit" and presses Enter
        }
        printf("you entered: %s", buffer);
    }
    return 0;
}