Running program from console with parameters [duplicate] - c

Question

This question already has answers here:
Command-line Parameters in C program?
(5 answers)
Closed 6 years ago.
My question is how to write a fuction with which I will can run a program from console with following parameters:
program.exe -i input.txt -o output.txt -t 1/2/3
#include <stdio.h>
#include <stdlib.h>
char substitute(char letter, char* cipher)
{
int i;
int cipher_length = strlen(cipher);
char substitution = letter;
for(i = 0; i < cipher_length; ++i)
{
if(cipher[i] == substitution)
{
substitution = cipher[(i%2) ? (i-1) : (i+1)];
break;
}
}
return substitution;
}
int main()
{
char c;
int t;
FILE *plik = fopen( "input.txt", "rt" );
FILE *encoded=fopen("output.txt","wt");
char* cipher1 = "GADERYPOLUKIgaderypoluki";
char* cipher2 = "POLITYKARENUpolitykarenu";
char* cipher3 = "KACEMINUTOWYkaceminutowy";
printf("Choose the cipher\n");
printf("[1]GA-DE-RY-PO-LU-KI\n");
printf("[2]PO-LI-TY-KA-RE-NU\n");
printf("[3]KA-CE-MI-NU-TO-WY\n");
scanf("%d",&t);
while(c != EOF)
{
c = getc( plik );
switch(t)
{
case 1:
putc(putchar(substitute(c, cipher1)),encoded);
break;
case 2: putc(putchar(substitute(c, cipher2)),encoded);
break;
case 3: putc(putchar(substitute(c, cipher3)),encoded);
break;
}
}
fclose( plik );
fclose(encoded);
}
I was given sth like this, but I don't know how to use it:
int function(int argc, char*argcv[])
{
int i;
char *string,*input,*output;
for(i=0; i<argc; i++)
{
}
return 0;
}

Answer 1

The parameter int argc contains the number of parameters in the command line.
The parameter char *argv[] is an array with all the strings typed in the command line.
This way, you can retrieve the command line parameters as:
int main(int argc, char *argv[]) {
int i = 0;
for (i = 0; i < argc; i++) {
printf("parameter %d = %s\n", i, argv[i]);
}
}
You can handle then the parameters passed in the command line:
int main(int argc, char *argv[]) {
int i = 0;
for (i = 0; i < argc; i++) {
...
if (strcmp(argv[i], "-i") == 0) {
doSomething(argv[i+1]);
}
...
}
}
To break the string you can use the following code:
// ...
char buffer[256];
char *p1 = NULL;
char *p2 = NULL;
int value = 0;
char old = 0;
strcpy(buffer, argv[7]);
p1 = buffer;
p2 = buffer;
do {
// parse until the delimiter
while (*p1 != '/' && *p1 != '\0') {
p1++;
}
// save delimiter value
old = *p1;
// convert the string to int
*p1 = '\0';
value = atoi(p2);
p1++;
// do something with the value
printf(">> value %d\n", value);
// goto the next token
p2 = p1;
} while (old != '\0');