Better Assert in C - c

Question

Sometimes I have to send the result of an assert over canbus, sometimes its local.
I use C only, Embitz compiler using GCC, STM32F407 or STM32F103.
My present assert is:
.h file:
extern char *astrbuf;
#define assert(left,operator,right)\
if(!((left) operator (right))) \
{asprintf(&astrbuf,"\nAssert error %s %d %ld %ld\n",__FILE__, __LINE__,\
(u32)(left),(u32)(right));\
asserted();\
}
.c file:
void asserted(void)
{ dprint("%s",astrbuf);
followed by the display code or canbus code.
Example:
assert(millis,<,maxtime);
This works very well, but will be better if the operator can be indicated.
I simply do not see how to display or send the operator, which can be ==, <, or >.

Answer 1

Why not use the standard assert interface and include the whole expression?
#define assert(EXPR) \
if (!(EXPR)) \
{asprintf(&astrbuf, "\nAssert error %s %d %s\n",__FILE__, __LINE__, #EXPR); \
asserted(); \
}
... using the # macro stringification operator.
By the way, why is half of your code in the macro and the other half in the asserted function? Why not do it all in one place?
#define assert(EXPR) \
if (!(EXPR)) \
{ \
asserted(__FILE__, __LINE__, #EXPR); \
}
with
void asserted(const char *file, int line, const char *expr) {
char *astrbuf;
asprintf(&astrbuf, "%s: %d: assertion failed: %s\n", file, line, expr);
dprint("%s", astrbuf);
...
}
Now you don't need a global variable anymore.
There's another potential issue. If you use your macro like this:
if (foo())
assert(x > 42);
else
bar();
... the else bar(); part will attach to the if statement hidden in assert, not the outer if. To fix this, you can wrap the whole thing in a do while loop:
#define assert(EXPR) \
do { \
if (!(EXPR)) { \
asserted(__FILE__, __LINE__, #EXPR); \
} \
} while (0)
Or alternatively make sure the whole macro expands to a single expression:
#define assert(EXPR) \
((void)((EXPR) || (asserted(__FILE__, __LINE__, #EXPR), 0)))
Of course you could also put the conditional logic in the function:
#define assert(EXPR) asserted(!!(EXPR), __FILE__, __LINE__, #expr)
void asserted(int cond, const char *file, int line, const char *expr) {
if (cond) {
return;
}
...
}

Answer 2

You can use the stringizing operator # to convert the macro parameter operator to a string #operator:
extern char *astrbuf;
#define assert(left,operator,right)\
if(!((left) operator (right))) \
{asprintf(&astrbuf,"\nAssert error %s %d %ld %s %ld\n",__FILE__, __LINE__,\
(u32)(left), #operator, (u32)(right));\
asserted();\
}

Answer 3

Perhaps you could try a slightly different approach to achieve the same goal.
Instead of passing (left, operator, right) into the macro, try passing a single boolean condition. You can use the condition inside of your actual assert function and also stringify it using macros. This way you can still report the whole condition to your debug module (canbus).
This will also work for more complicated expressions like ((a-b)< 0)
#define assert( condition ) custom_assert( condition , STRINGIFY_CONSTANT( condition ), __FILE__, __LINE__)
The stringify macro is in its own header file and was derived based on this link. https://gcc.gnu.org/onlinedocs/gcc-3.4.3/cpp/Stringification.html
#define STRINGIFY_CONSTANT(a) STRINGIFY_CONSTANT_DO_NOT_USE(a)
#define STRINGIFY_CONSTANT_DO_NOT_USE(a) #a
Obviously, don't use STRINGIFY_CONSTANT_DO_NOT_USE
void custom_assert( int condition , const char * condition_string, const char * file_name, int line_number)
{
if (!condition)
{
dprint("Assert Failed:'%s' File:'%s' Line:'%d'",condition_string, file_name, line_number);
}
}
I would avoid putting anything more than a single function call into your assert #define as that can be hard to debug and it will also increase the size of your code. I recommend putting any logic into the function.
I called my assert custom_assert. I also have many #defines to put the debug output to different channels like usb, rs232, a on screen display, etc. In release mode the asserts just reboot the embedded device, which is acceptable in my application.

Answer 4

Assert is a macro, the way I understand it, it is always inline.
The code for the machine has lots of asserts to prevent damage, therefore one needs to keep the code as fast as possible, ie. inline under normal circumstances.
When anything goes wrong, the function asserted is used, speed is no more a problem, safety is. The function asserted switches off motors, etc, and reports over canbus or local display. No way I want to do all that in a macro.
That is why part of the code is in a macro, part in a function.
Please correct me if my understanding is wrong.
Not having a global variable is a definite plus, and I have added the while (0), as in other macros.