Are the strings in argv modifiable?

Question

I just wrote a small program that reads command line arguments in C, nothing too difficult. I was also modifying them, for example changing the first character of the parame

Answer 1

The arrays that support the strings in argv are modifiable.
But you have no way to know their sizes.

I would frown upon seeing code that (tries to) increase the size of the strings.

#include 
#include 
// this program may behave erraticaly
int main(int argc, char **argv) {
    for (int k = 1; k < argc; k++) {
        printf("original argv[%d] is %s\n", k, argv[k]);
    }
    printf("\n");
    for (int k = 1; k < argc; k++) {
        strcat(argv[k], " foo"); // add foo to each argv string
        printf("first modification to argv[%d] is %s\n", k, argv[k]);
    }
    printf("\n");
    for (int k = argc; k > 1; k--) {
        strcat(argv[k - 1], " bar"); // add bar to each argv string
        printf("final argv[%d] is %s\n", k - 1, argv[k - 1]);
    }
    return 0;
}

On my machine, calling that program with one two three arguments produces

original argv[1] is one
original argv[2] is two
original argv[3] is three

first modification to argv[1] is one foo
first modification to argv[2] is foo foo
first modification to argv[3] is foo foo

final argv[3] is foo foo bar
final argv[2] is foo foo foo bar bar
final argv[1] is one foo foo foo bar bar bar