Using variable input for system()

Question

I am using an executable made from C, and I am trying to pass variables in R to it.

C code:

#include <stdio.h>
#include <stdlib.h>
int sumUp(int x, int y, int z, int *sum);

int main()
{
    int x1,x2,x3;
    int total = 0;

    scanf("%d %d %d",&x1,&x2,&x3);
    sumUp(x1,x2,x3,&total);
    printf("Your total is :%d\n", total);

    system("pause");

}

int sumUp(int x, int y, int z, int *sum)
{
    *sum = x + y + z;
}

and Here is my R code:

x <- 0
y <- 0
z <- 0

readint <-function(){
  a <- readline(prompt = "Enter a number: \n")
}

x <- as.numeric(readint())
y <- as.numeric(readint())
z <- as.numeric(readint())

system("Practice.exe", intern = TRUE,input = "x y z")

I am having an issue when I use variables for input as it will print an incorrect value. However, when I use direct input, like input = "1 2 3", I will get the correct answer. I checked the types for for my variables, and they seem to be correct. Here is the output for reference:

Is there something wonky going on between R and C, or am I doing something incorrect with system? Even if I vary the values of x,y,z, I will get 84. So I imagine there is something going on under the hood here that I am missing. I tried using args instead of input, but ran into the same issue, except that it gave a value of 126 no matter what I entered, variable or directly. Any help is appreciated, thank you.

First thing first, remove system("pause") from your C code, it has no place in non-interactive programs and is unnecessary beyond that in 99.99% of cases. Secondly, you’re using the input parameter incorrectly in R. You’re supposed to pass a character vector of the actual values here, not of variable names. — Konrad Rudolph
– Konrad Rudolph, Commented Jun 3, 2019 at 16:47
Third, quoting the help page, system2 is recommended for new code. — Rui Barradas
– Rui Barradas, Commented Jun 3, 2019 at 16:52
@KonradRudolph Is there a proper way to pass input to an executable by variable name? — hkj447
– hkj447, Commented Jun 3, 2019 at 16:54
@hkj447 You need to pass the values. Check out the paste function for converting multiple values to string and concatenating them. — Konrad Rudolph
– Konrad Rudolph, Commented Jun 3, 2019 at 16:55

Fausto Carvalho Marques Silva · Accepted Answer · 2019-06-03 17:46:18Z

1

I rather do this in C:

#include <stdio.h>
#include <stdlib.h>
int sumUp(int x, int y, int z, int *sum);

int main()
{
    int x1,x2,x3;
    int total = 0;
    x1 = strtol(argv[1], NULL, 10);
    x2 = strtol(argv[2], NULL, 10);
    x3 = strtol(argv[3], NULL, 10);

    sumUp(x1,x2,x3,&total);
    printf("Your total is :%d\n", total);

    system("pause");

}

int sumUp(int x, int y, int z, int *sum)
{
    *sum = x + y + z;
}

And this in R:

x <- 0
y <- 0
z <- 0

readint <-function(){
  a <- readline(prompt = "Enter a number: \n")
}

x <- as.numeric(readint())
y <- as.numeric(readint())
z <- as.numeric(readint())
cmd <- paste("Practice.exe", x, y, z)
system(cmd, intern = TRUE)

edited Jun 3, 2019 at 17:46

answered Jun 3, 2019 at 17:39

Fausto Carvalho Marques Silva

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