In previous example, test_cstring_run function does not test anything. Let us add some test as following.
static int test_cstring_run(void *priv)
{
struct priv_data *data = priv;
cstring *cstr = data->cstr;
printf("\ttest_cstring_run\n");
if (cstr->length(cstr) != 16) {
printf("length failed\n");
}
if (cstr->max_size(cstr) != 64) {
printf("max_size failed\n");
}
if (cstr->at(cstr, 3) != 't') {
printf("at failed\n");
}
return 0;
}
It checks if return values of length, max_size and at methods.
There is a pettern for all if-statements. It only compares two values and prints a message. We have made a macro to replace a repeated if-else-statement and for-loop before. What about making a macro to replace the if-statement as following?
#define CHECK_TEST(__condition, __msg) ({ \
int ____ret_error = !!(__condition); \
if (____ret_error) printf("<%s:%d> %s\n", \
__FILE__, __LINE__, __msg); \
})
static int test_cstring_run_macro(void *priv)
{
struct priv_data *data = priv;
cstring *cstr = data->cstr;
printf("\ttest_cstring_run\n");
CHECK_TEST(cstr->length(cstr) != 16, "length failed\n");
CHECK_TEST(cstr->length(cstr) == 16, "length ok\n");
return 0;
}
static struct unittest test_cstring2 = {
.init = test_cstring_init,
.final = test_cstring_final,
.run = test_cstring_run_macro,
.priv = &pdata,
};
Now we use printf to print a message but it would be necessary to print a message on log file. If we make a macro to check values and print a message, it will be more flexible to print error messages. And of couse, the test function will be shorter.
Let us see the CHECK_TEST macro.
!!(__condition) statement might be strange for someone.
It translates any statement into the logical values: 0 or 1.
Let us look into it step by step.
(__condition): return the value of a statement.(cstr->length(cstr)returns a integer value.!(__condition): ! means NOT. What is "NOT" of a integer value? If the value is 0, it is 1. If the value is not 0, it is 0. Therefore !() translates a arithmatic value into a logical value.!(cstr->length(cstr))will be 0, if the length is 16.
!!(__condition): What is NOT of NOT? It is nothing. So this is a final logical value. If the integer value of the condition is not zero, this is 1 (TRUE), and vice versa.
Please notice that the macro function has a local variable.
That is what the macro is wrapped with ({..}).
It called as the compound statement of GCC compiler.
- compound statement: http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs
If you would like to know more about the compound statement please read kernel code:
If you use another compiler, you can use do-while as following.
#define CHECK_TEST(__condition, __msg) do { \
int ____ret_error = !!(__condition); \
if (____ret_error) printf("<%s:%d> %s\n", \
__FILE__, __LINE__, __msg); \
} while (0);