In the early days of K&R C programming the type for functions parameters was optional and declared separately:

void old(a, b, c)
 int a;
 bool b;
 char *c;
{
 printf("a=%i b=%d c=%p\n", a, b, c);
}

For ANSI C the syntax was changed, which allows the types to be specified directly before the arguments:

void new(int a, bool b, char *c) {
 printf("a=%i b=%d c=%p\n", a, b, c);
}

They nearly looks the same, but there is a subtile draw-back to the old syntax: The gcc compile will not report an error if you do not specify all arguments:

#include <stdio.h>
#include <stdbool.h>
int main(void) {
#if 1
 old(); /* missed ? */
 old(0); /* missed ? */
 old(0, false); /* missed ? */
#endif
 old(0, false, ""); /* okay ? */
#if 1
 new(); /* error ? */
 new(0); /* error ? */
 new(0, false); /* error ? */
#endif
 new(0, false, ""); \* okay ? */
 return 0;
}

Even a -Wall -pedantic -ansi -Werror will not find it. Using clang on the other hand reports an error.

So watch out if you for example look at CrudeSAML, which uses both syntax at the same time.

PS: It you ask yourself what values are passed if they are not specified: random data respectively whatever is currently on your stack; so this is a security vulnerability as it discloses the content of your stack, which might contain confidential data.