C：fgets（）和命令行输入

Question

I'm trying to write a program that handles processes. The user will be prompted..

shell: start emacs file.c
Process 346 has started.

I'm having a few issues with fgets, since I don't know what to put as my third argument (I want it to take in from the command line/argv) with

fgets(buffer, 4096, How can I do a file pointer if I'm not doing a file, just argv?)

int main(int argc, char **argv)   
{
 while(1) {
    printf("shell: ");   
int status, pid;
int i=0;
char buffer[4097];
    fgets(buffer, 4096, ???? ) //I want it to take in from argv. Do I need to declare 4096?

if(strcmp(argv[1],"start") == 0 )
    { printf("myshell: process has started \n");
           while (str = strtok(buffer," ") = NULL)  //??? What do I declare str as?
            argv[i] = str;    
            i = i+1;
            }      

            if ((pid = fork()) < 0) {  //Child process fork
            perror("fork");       
            exit(1);
            }
            if (pid == 0) {  //Child executes code
            execvp(argv[0], argv );
            perror(argv[1]);    //argv1? 
            exit(1);
             }
    }

Does this make sense fort the desired behavior explained above? I'm not entirely sure of the location of my while loop that has strtok, didn't know if that maybe has to be outside of the if-statement.

Also, is it correct for my strtok function to be called as strtok(buffer, " ")? Thank you.

Answer 1

 I don't know what to put as my third argument ??

From the man page,
char *fgets(char * restrict s, int n, FILE * restrict stream);

So third argument is FILE pointer. Since argv is pointer to string, you can't use in fgets() as mentioned.

you can directly use or copy to some local buffer using strcpy() family of functions.

Answer 2

You are going wrong entirely my friend when you will start program through terminal (./your_program argv1 argv2 ... argvN) argv is passed by system to the main function, but after starting the program nothing will going store in argv ie

./your_program argv1 argv2 //here you can collect string input from system shell: start emac file.c //this will not stored into argv

to take value those value you can something do like that fgets(buffer, 4096,stdin) // from console into your buffer not in argv

and after that you can use string tokeniser function to take each value from buffer I do not know exact syntax or program for string tokeniser but this link will help you http://www.cplusplus.com/reference/cstring/strtok/