How to evaluate part of an expression using macros in C? - c

Question

I am currently developing a unit test library in C and I wanted to add a functionality Catch (in C++) had.
When you do, using Catch :
int x = 5;
REQUIRE(x == 4);
The output will be something like this :
Failed statement : x == 4
evaluated as 5 == 4
Is it possible to do something like that in C ?
This needs to be done at runtime.

Answer 1

You could do something like this. It's not very convenient, but it works:
#include <stdio.h>
#include <stdlib.h>
#define ASSERT_INT 1
#define ASSERT_EQ(x,y,type) do { if((x)!=(y)) { \
switch(type) { \
case ASSERT_INT: \
printf("Failed statement : %s == %d\n\tevaluated as %d == %d\n", \
#x, (y),(x), (y)); break; \
} exit(EXIT_FAILURE); }} while(0)
It requires some work though. If you want many operations you can do like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ASSERT_INT 1
#define ASSERT_EQ 1
#define ASSERT(x,y,op,type) do { \
int success; \
char op_str[3]; \
switch(op) { \
case ASSERT_EQ: \
strcpy(op_str, "==");success = ((x) == (y)); break; \
} \
if(!success) { \
switch(type) { \
case ASSERT_INT: \
printf("Failed statement : %s %s %d\n\tevaluated as %d %s %d\n", \
#x, op_str, (y),(x), op_str, (y)); break; \
} exit(EXIT_FAILURE); }} while(0)
And the output:
$ ./a.out
Failed statement : x == 4
evaluated as 5 == 4
You will need to add a modified version of strcpy(op_str, "==");success = ((x) == (y)); break; for each different logical operation and a modified version of printf("Failed statement : %s %s %d\n\tevaluated as %d %s %d\n", #x, op_str, (y),(x), op_str, (y)); break; for each different type.