如何使用argv [1]作为预定义的宏？

Question

[Coding in POSIX, using Geany in Ubuntu]

I have these classes: main.c , Ac , Ah where Ah is included in main.c. I started all my project using a macro in Ac, namely #define PNUM 10 . I already defined structures, several arrays, I created threads and so on and eventually when I got everything done, I decided to ask the user to enter an integer as PNUM using argv in main.c file. ( PNUM determines the number of threads that I'm going to deal with.)

• I don't want to pass this value to Ac file using functions in main.c: I tried so but it's my first experience in POSIX and the level of difficulty went over my knowledge.

• I know that #define PNUM 10 is a symbolic name to numeric constants and cannot be reassigned at all. I also don't insist on keeping this line of my code, however, it seems crucial here.(eg creating PNUM number of threads in initialization step and allocating memory to arrays of condition variables, etc.)

• My question seems to have an easy and straightforward answer but I am not very comfortable with C .

---

The general scheme: All functions mentioned in Ac need to know PNUM.

main.c

#include "philos.h"

void* philosopher(int *);
void* waiter(int *);

int main(int argc, char** argv)
{
    int philNum = atoi(argv[1]);
    void * tab = tableinit(philosopher, waiter);
    return 0;
}

void * philosopher(int * who)
{   ...
    pickup((*who));
    putdown((*who));
    ...
}
void * waiter(int * who)
{   ...
    replaceBottles();
    refillBowls();
    ...
}

---

Ac

#define PNUM 10
#define WAITERNUM 2
typedef struct tablestruct
{
    pthread_t t[PNUM];
    pthread_t w[WAITERNUM];
    int self[PNUM];
    int wself[WAITERNUM];
    pthread_mutex_t mutex;
    pthread_cond_t condition[PNUM];
    philstat status[PNUM];
    int snack_wine[PNUM];
 }table;
void printstate(){...}
void pickup(int k){...}
void putdown(int k){...}
int test (int i){...}
int consumptions(int i){...}
int finishedServing(int){...}
void replaceBottles(int){...}
void refillBowls(int){...}
table * tableinit(void *(* philosopher)(void *), void*(* waiter)(void *)){...}

Answer 1

The question as it stands doesn't quite work. You can't take user input and use it as a macro. You know this: "...numeric constants and cannot be reassigned". As in, it's never going to be anything other than 10.

So if you want the number of threads to vary depending on user-input, you're not going to be able to use a macro.

I mean, you could do something lame like #define PNUM global_num_threads or '#define PNUM getNumThreads()`, and add a global or a function to go get that variable. While that might be the.... least intrusive into your codebase, it's a bad design that indicates rot. If you're going to make this sort of change to the code, do it right.

Yeah, even though it "seems crucial" to use a macro, it's not. You can swap that out with a variable.

And passing variables is almost fundamental, so get used to it.