如何在C程序中重定向多个文本文件

Question

How to redirect more than one text file in c program? For example I have the following C code:

//redirection.c
#include<stdio.h>
main()
{
int x,y;
scanf("%d",&x);
x=x*x;
printf("%d",x);

scanf("%d",&y);
y=x+y;
printf("%d",y);
}

After compiling this code I created two text files text1.txt having the value 8 and text2.txt having the value 6.

When I give input to this program using command line redirection (as redirection<text1.txt ), it gives output 64 and does not wait to take another input (and program exits) which I want to give another input from text2.txt.

Is there any solution how can I send another input via text2.txt for second scanf function in the above program?

Answer 1

While giving the input as redirection as like this.

cat a b | ./a.out.

Or else you can use the command line arguments.

#include<stdio.h>
main(int argc, char *argv[])
{
    FILE *fp, *fp1;
    if ( (fp=fopen(argv[1],"r")) == NULL ){
            printf("file cannot be opened\n");
            return 1;
    }
    if (( fp1=fopen(argv[2],"r")) == NULL ){
     printf("file cannot be opened\n");
            return 1;
    }
    int x,y;
    fscanf(fp,"%d",&x);// If you having  only the value in that file
    x=x*x;
    printf("%d\n",x);
    fscanf(fp1,"%d",&y);// If you having  only the value in that file                                       
    y=x+y;
    printf("%d\n",y);

}

Answer 2

you can also use command line arguments:

#include <stdio.h>

#define BUFSIZE 1000

int main(int argc, char *argv[])
{
    FILE *fp1 = NULL, *fp2 = NULL;
    char buff1[BUFSIZE], buff2[BUFSIZE];

    fp1 = fopen(argv[1], "r");
    while (fgets(buff1, BUFSIZE - 1, fp1) != NULL)
    {
        printf("%s\n", buff1);
    }
    fclose(fp1);

    fp2 = fopen(argv[2], "r");
    while (fgets(buff2, BUFSIZE - 1, fp2) != NULL)
    {
        printf("%s\n", buff2);
    }
    fclose(fp2);
}

here is a more cleaned up version:

#include <stdio.h>

#define BUFSIZE 1000
void print_content(char *file);
int main(int argc, char *argv[])
{
    print_content(argv[1]);
    print_content(argv[2]);
}

void print_content(char *file){
    char buff[BUFSIZE];
    FILE *fp = fopen(file, "r");

    while (fgets(buff, sizeof(buff), fp) != NULL)
    {
        printf("%s\n", buff);
    }
    fclose(fp);
}