How to send command to Linux command from C program

Question

I am trying to send a command to a Linux command line from a C program and there is one part I am not sure how to do.

For example in my C code I have

system("raspistill -o image.jpg");

What I would like to be able to do is add a number to the end of "image" and increment it every time the program runs, but how can I pass in a variable n to the system() function that is only looking for a const char ?

I tried this but it did not work:

char fileName = ("raspistill -o image%d.jpg",n);
system(filename);

I've tried searching on this and haven't found anything about how to add a variable to it. Sorry for the noob question.

Answer 1

char fileName[80];

sprintf(fileName, "raspistill -o image%d.jpg",n);
system(filename);

Answer 2

First, a String is a char array, so declare (I think you know, just to emphasize):

char command[32]; 

So, simple solution will be:

sprintf(command, "raspistill -o image%d.jpg", n);

Then call system(command); . This is just what you need.

---

EDIT:

If you need program output , try popen :

char command[32]; 
char data[1024];
sprintf(command, "raspistill -o image%d.jpg", n);
//Open the process with given 'command' for reading
FILE* file = popen(command, "r");
// do something with program output.
while (fgets(data, sizeof(data)-1, file) != NULL) {
    printf("%s", data);
}
pclose(file);

Sources: C: Run a System Command and Get Output?

http://man7.org/linux/man-pages/man3/popen.3.html