linux application remote debugging without gdb - c

Question

I wrote a linux program as below:
int g_para1 = 10;
int g_para2 = 11;
void SetPara(int para1, int para2)
{
g_para1 = para1;
g_para2 = para2;
}
void DumpPara()
{
printf("g_para1 = %d, g_para2 = %d\n", g_para1,g_para2);
}
void init()
{
int pid;
if(pid = fork())
exit(0);
else if(pid < 0)
exit(1);
setsid();
if(pid = fork())
exit(0);
else if(pid < 0)
exit(1);
return;
}
int main()
{
signal(SIGCHLD, SIG_IGN);
init();
while(1)
{
DumpPara();
sleep(10);
}
return 0;
}
And then compile and run it in the shell
gcc -o test test.c
./test
it will show the print "g_para1 = 10, g_para2 = 11" every 10 seconds.
My question is:
If I execute "SetPara 20, 30" in the shell, i want the print shows "g_para1 = 20, g_para2 = 30".
What should i do to make it work?
If I do nothing, it will show
SetPara 20,30
SetPara: command not found

Answer 1

First, an application (in C, compiled with debug info, e.g. with gcc -Wall -g) can be remotely debugged. If you have ssh available, you simply debug using gdb thru a terminal connection via ssh. Otherwise, read the documentation of GDB, it has a chapter on remote debugging.
Then, it looks like you wish to embed your application into a scripting language interpreter. Then try lua, or GNU guile, or perhaps even python or ocaml. Notice that embedding your application inside an interpreter (or symetrically, putting an interpreter inside your application) is a heavy architectural decision and has major impacts on its design.
BTW, some Unix shells can be extended thru plugins, e.g. zsh (with modules...). Plugins use dynamic loading facilities like dlopen(3) (you might consider using them in your application).
But an ordinary shell can only start external programs using fork(2) & execve(2)
BTW, you might consider making your application behave as a Web server by using some HTTP server library inside it, e.g. libonion. You could also consider remote procedure call techniques, e.g. JSON RPC
Read also Advanced Linux Programming
As for your improved question, just define a convention in main arguments: you could want that if you invoke your program with arguments --setpara 23 45 it will call SetPara(23,45) e.g. with code like:
int main (int argc, char**argv) {
if (argc>3 && !strcmp[argv[1], "--setpara")) {
int x = atoi(argv[2]);
int y = atoi(argv[3]);
SetPara (x,y);
}
but you should do serious arguments passing e.g. with getopt_long (and accept --help & --version). See this answer and that one.
If you want SetPara to be called elsewhere in your code, the arguments to main should trigger other behavior (e.g. initializing global data, initializing an embedded interpreter, etc.).
Notice that each process has its own address space in virtual memory. See also this answer.
PS: your question is very unclear; I tried to give various ways of approaching your issues, which I am mostly guessing. You should study -for inspiration at least- the source code of some existing free software related to your goals.