C user dynamic input with argv

Question

So I try to take a user input of unknown max length from the command line. The program to be able to do something like that needs to take a dynamic input of a string (char array maybe?). The outcome should be something like

./a.out st1 your str is ...

the only code I was able to come up with is the following

int main (int argc, char* argv[]){
    ...
    char str1[];
    str1 = argv[1];
    printf("your...);
    ...
}

please specify your sample usage of the app and desired results. — Code Plus, Dec 19 '21 at 16:16
If you execute `a.out your string is the beaches of Corfu` then you want the output: `your string is the beaches of Corfu`, is that correct? — Beta, Dec 19 '21 at 16:20
Vlad I dont know what it has to do with the q but its an island in greek where I study — Angelo, Dec 19 '21 at 17:22
Are you asking how to use declare arrays in C, or... what? How to copy strings? — Lundin, Dec 20 '21 at 08:41

score 2 · Accepted Answer · edited Dec 19 '21 at 19:00

2

This declaration of a block scope array with an empty number of elements:

char str1[];

is incorrect. Moreover arrays do not have the assignment operator:

str1 = argv[1];

You could declare a pointer:

char *str1;
str1 = argv[1];
printf("your...);

edited Dec 19 '21 at 19:00

halfer

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answered Dec 19 '21 at 16:08

Vlad from Moscow

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score 0 · Answer 2 · answered Dec 19 '21 at 20:09

0

C will terminate argv with a null pointer, and argv is modifiable, so it's actually very easy to implement shift like in bash scripts. Your basis could look like the following.

#include <stdio.h>

int main(int argc, char *argv[]) {
    char *arg;
    if(!argc || !argv[0]) return 0; /* Defensive */
    while(arg = *(++argv))
        printf("do something with %s\n", arg);
    return 0;
}

answered Dec 19 '21 at 20:09

Neil

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Or you could write a readable loop instead of obscure pointer arithmetic: `for(int i=0; i – Lundin Dec 20 '21 at 08:47
True; not just about style, the way you propose is good if you want the index at which the argument occurs. – Neil Dec 20 '21 at 21:51

C user dynamic input with argv

2 Answers2