Wednesday 1 January 2020

io - How can one flush input stream in C?



I am not able to flush stdin here, is there a way to flush it? If not then how to make getchar() to take a character as input from user, instead of a "\n" left by scanf() in the input buffer??



#include "stdio.h"
#include "stdlib.h"


int main(int argc,char*argv[]) {
FILE *fp;
char another='y';
struct emp {
char name[40];
int age;
float bs;
};
struct emp e;
if(argc!=2) {

printf("please write 1 target file name\n");
}
fp=fopen(argv[1],"wb");
if(fp==NULL) {
puts("cannot open file");
exit(1);
}
while(another=='y') {
printf("\nEnter name,age and basic salary");
scanf("%s %d %f",e.name,&e.age,&e.bs);

fwrite(&e,sizeof(e),1,fp);

printf("Add another record (Y/N)");
fflush(stdin);
another=getchar();
}
fclose(fp);
return 0;
}



EDIT: updated code, still not working properly



#include "stdio.h"
#include "stdlib.h"

int main(int argc,char*argv[]) {
FILE *fp;
char another='y';
struct emp {

char name[40];
int age;
float bs;
};
struct emp e;
unsigned int const BUF_SIZE = 1024;
char buf[BUF_SIZE];

if(argc!=2) {
printf("please write 1 target file name\n");

}
fp=fopen(argv[1],"wb");
if(fp==NULL) {
puts("cannot open file");
exit(1);
}
while(another=='y') {
printf("\nEnter name,age and basic salary : ");
fgets(buf, BUF_SIZE, stdin);
sscanf(buf, "%s %d %f", e.name, &e.age, &e.bs);

fwrite(&e,sizeof(e),1,fp);
printf("Add another record (Y/N)");
another=getchar();
}
fclose(fp);
return 0;
}


Output:




dev@dev-laptop:~/Documents/c++_prac/google_int_prac$ ./a.out emp.dat

Enter name,age and basic salary : deovrat 45 23
Add another record (Y/N)y

Enter name,age and basic salary : Add another record (Y/N)y

Enter name,age and basic salary : Add another record (Y/N)


Answer



Update: You need to add another getchar() at the end of your loop to consume the '\n' that follows the Y/N. I don't think this is the best way to go, but it will make your code work as it stands now.



while(another=='y') {
printf("\nEnter name,age and basic salary : ");
fgets(buf, BUF_SIZE, stdin);
sscanf(buf, "%s %d %f", e.name, &e.age, &e.bs);
fwrite(&e,sizeof(e),1,fp);
printf("Add another record (Y/N)");
another=getchar();

getchar();
}


I would suggest reading the data you want to parse (up to and including the '\n') into a buffer and then parse it out using sscanf(). This way you consume the newline and you can perform other sanity checks on the data.


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