Learning goals

You will learn the following concepts/skills:

1. C preprocessor − how to use several of the most commonly used directives
   1. #define symbols – not just for defining constants
   2. #define macros – like functions but with special capabilities
   3. #include guards – enable more versatile use of header (.h) files.

Overview

For this part, you will create a reusable library for debugging any C project. When you are done, you will use log_int(…) to print an int variable, log_float(…) to print a float variable, log_str(…) to print a str variable, log_char(…) to print a char variable, log_addr(…) to print any address variable (e.g., char*, int*, etc.), log_bool(…) to print a bool variable, You will use these similarly to the way some people use printf(…), but these macros will generate code that prints the variable name (or expression) as well as the value. For example, invoking log_int(3 + 4) will generate the C code printf("%s == %d\n", "3 + 4", 7), which will print 3 + 4 == 7.

For this part, you will create a reusable library for debugging any C project. In the process, you will learn about the C preprocessor.

Instructions

How much work is this?

Requirements

Submit

To submit HW06 from within your hw06 directory, type 264submit HW06 log_macros.h

Pretester

Q&A

1. Should I have a semicolon at the end of a #define macro

   No. The person using the macro will normally include the semicolon.

2. What does #x do in a #define macro

   It expands to the text of the expression, instead of its value. This is easiest to see if you test using the 264cpp (or /usr/bin/cpp) command.
   Here is an example, which uses the log_int(…) snippet given in the Requirements table.

   // demonstrate_hash.c
   #include <stdio.h>
   #include <stdlib.h>
   
   #define log_int(n) printf("%s == %d\n", (#n), (n))
   
   int main(int argc, char* argv[]) {
       log_int(3 + 3);
       return EXIT_SUCCESS;
   }
   

   If we process that with the preprocessor directly (instead of via gcc), we can see what it becomes. Note: 264cpp is just a shortcut for /usr/bin/cpp ▒▒▒ | indent -kr that also cleans up the output a bit to make it easier to read.
   you@ecegrid-thin1 ~/HW06 $ /usr/bin/cpp demonstrate_hash.c | indent -kr

   … int main(int argc, char* argv[]) { printf("%s == %d\n", ("3 + 3"), (3 + 3)); return 0; }
   Notice that the second argument to printf(…) is a string literal, "3 + 3"—the text of the argument that was passed to log_int(…). That is different from the third argument, which is the value of that parameter, 3 + 3 (= 6).

3. GCC: “error: ‘true’ undeclared” ⋯???
   GCC: “error: ‘false’ undeclared” ⋯??

   The true and false constants are defined in a standard header called stdbool.h; you need to include it (i.e., #include <stdbool.h>) in any file where you use them (e.g., log_macros.h). true, and false.

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