Help50

Human `help50`

Problem

If not yet familiar, help50 is a command line tool included with CS50 IDE that makes an effort to translate some of the more arcane error messages that other tools, such as clang or valgrind, sometimes spit out. In this way, it serves as a "virtual TF" of sorts, hopefully helping nudge students in the right direction, so that they needn’t wait for a staff member at office hours when a little bit of translation of the error message is really all that’s needed to move on.

If you aren’t familiar with help50 just yet, now is the time! Here’s an example of a simple broken C file, rocket.c, which is supposed to count down from 10 and then print blastoff!:

#include <stdio.h>

int main(void)
{
    int i;
    for(i = 10; i > 0; i--);
    {
        printf("%i... ", i);
    }
    printf("blastoff!\n");
}

Copy this code exactly into your IDE (even if you’ve already spotted the problem) and try to compile this program with make rocket. You should receive the following output from clang:

rocket.c:6:28: error: for loop has empty body [-Werror,-Wempty-body]
    for(int i = 10; i > 0; i--);

Hmm… that for loop’s body looks awfully populated to me; maybe help50 can make some sense of it? Let’s attempt to recompile rocket, but this time prepend the command with help50. Perhaps this error message sheds more light onto the problem:

Helping with...

rocket.c:6:28: error: for loop has empty body [-Werror,-Wempty-body]

Try removing the semicolon directly after the closing parentheses of the for loop on line 6 of rocket.c.

Ahh, that helps! If you remove the semicolon and attempt to recompile, everything works as expected.

help50 works because the staff has written a series of "matchers" for different errors into its source code. Basically, we’ve written code that looks for certain types of error messages that clang or valgrind might output, and when one of those matchers, well, matches what we’re looking for, it outputs a more human-friendly translation of that message. Unfortunately, it seems the number of errors these programs can spit out is quite large, and help50 doesn’t yet have so-called "matchers" for all types of errors. In those cases, it’ll just tell you that it doesn’t know what to say.

Put yourself in the shoes of a TF or CA at office hours. If you see errors like the five below (which you or your classmates have actually experienced this semester!), how would you advise help50 to respond? A friendly one- or two-sentence note for each should suffice!

Problem Set 1:

mario.c:19:27: error: invalid conversion specifier '
' [-Werror,-Wformat-invalid-specifier]
                printf("%#\n", i);
                        ~~^

Problem Set 2:

initials.c:13:10: error: definition of variable with array type needs an explicit size or an initializer
    char initials[];
         ^

Problem Set 3:

find.c:53:16: error: non-object type 'bool (int, int *, int)' is not assignable
    if (search = true)
        ~~~~~~ ^

Problem Set 4:

recover.c:22:10: error: variable 'blockptr' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
     if (cardptr == NULL)
         ^~~~~~~~~~~~~~~

Problem Set 5:

dictionary.c:146:36: error: passing 'const char *' to parameter of type
      'char *' discards qualifiers
      [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
    int hash_value = hash_function(word);
                                    ^~~~

Sample Solution

Human help50 (sample solution)

Human help50

Problem

Sample Solution

Human `help50`