Testing and Debugging

Diagnostic Log

A debug flag can print the values that explain how a result was produced.

debug flag A flag lets diagnostic output be turned on while leaving the normal result unchanged.
trace value Printing intermediate values can confirm which path the program followed.

Diagnostic Log

debug
diagnostic_log.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    int debug = 1;
    int width = 6;
    int height = 4;
    int area = width * height;

    if (debug) {
        printf("debug width=%d height=%d\n", width, height);
    }

    printf("area=%d\n", area);
    return 0;
}

#include <stdio.h>

int main(void) {
    int debug = 0;
    int width = 6;
    int height = 4;
    int area = width * height;

    if (debug) {
        printf("debug width=%d height=%d\n", width, height);
    }

    printf("area=%d\n", area);
    return 0;
}

  1. debug ← 1, width ← 6, height ← 4, area ← 24

    3int main(void) {4    int debug→ 1 = 1; //@debug=0, 15    int width→ 6 = 6;6    int height→ 4 = 4;7    int area→ 24 = width6 * height4;

  2. if (debug)

    9if (debug1) {10    printf("debug width=%d height=%d\n", width6, height4);11}
    outputdebug width=6 height=4

  3. printf("area=%d ", area);

    13    printf("area=%d\n", area24);14    return 0;15}
    outputarea=24

  1. debug ← 0, width ← 6, height ← 4, area ← 24

    3int main(void) {4    int debug→ 0 = 0;5    int width→ 6 = 6;6    int height→ 4 = 4;7    int area→ 24 = width6 * height4;89    if (debug) {10        printf("debug width=%d height=%d\n", width, height);11    }1213    printf("area=%d\n", area24);14    return 0;15}
    outputarea=24