How to modify contents in a file? - c

Question

I am a complete beginner of C. My problem is to modify a content in a file.
I am writing two files and then merge the contents of the two files in a another file. This another file is the one I need to modify.
what to modify?
The myfile1.txt values are 199112345671273 and the myfile2.txt values are 24AUS2024MED712.
The merging file (myfile3.txt) has 19911234567127324AUS2024MED712
The thing that I need to modify is the values of myfile2.txt. I want to hide its values in asterisk so when reading myfile3.txt,I get the following
199112345671273****************
my logic is messed up. I just want to stores both values of myfile1 and myfile2. then display myfile3 in condition that myfile2 has to be hidden in asterisk when reading.
My write.c program - write data in two files
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 100
int main (int argc, char **argv) {
char registration[MAX_SIZE], location[MAX_SIZE], faculty[MAX_SIZE];
int birthOfYear, birthOfMonth, birthOfDate, layerArch1, layerArch2, levelOfStudy, graduatingYear;
FILE *fptr, *anotherfptr;
fptr = fopen("myfile01.txt","w");
anotherfptr = fopen("myfile02.txt", "w");
if(fptr == NULL) {
printf("Error!");
exit(1);
}
printf("Enter a registration number (XXXXXX): ");
scanf("%s", registration); //read as a string
printf("Enter location (location as in currency, AUS CND SIN: ");
scanf("%s", location); //read as a string
printf("Enter faculty (ENG BUS SCI MED): ");
scanf("%s", faculty); //read as a string
printf("Enter birth of year (19XX 200X): ");
scanf("%d", &birthOfYear);
printf("Enter birth of month (XX): ");
scanf("%d", &birthOfMonth);
printf("Enter birth of date (XX): ");
scanf("%d", &birthOfDate);
printf("Enter level of study (1 -first, 2- second, 3- third, 4-fourth, 5 - other): ");
scanf("%d", &levelOfStudy);
printf("Enter graduating year (XXXX): ");
scanf("%d",&graduatingYear);
printf("Enter layer of Architecture 1 (0-sensing, 1-network, 2-smart(hidden), 3-devices): ");
scanf("%d",&layerArch1);
printf("Enter layer of Architecture 2 (0-sensing, 1-network, 2-smart(hidden), 3-devices): ");
scanf("%d",&layerArch2);
fprintf(fptr,"%d%s%d%d%d", birthOfYear, registration, birthOfMonth, birthOfDate, layerArch1); //writing into file with some formatting
fclose(fptr);
fprintf(anotherfptr,"%d%d%s%d%s%d%d", layerArch2, levelOfStudy, location, graduatingYear, faculty, birthOfDate, birthOfMonth);
//writing into file with some formatting
fclose(anotherfptr);
return 0;
}
my merge.c program - to merge two files
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
FILE *fs1, *fs2, *ft;
char ch, file1[200], file2[200], file3[200];
printf("Enter name of first file\n");
gets(file1);
printf("Enter name of second file\n");
gets(file2);
printf("Enter name of file which will store contents of the two files\n");
gets(file3);
fs1 = fopen(file1, "r");
fs2 = fopen(file2, "r");
if(fs1 == NULL || fs2 == NULL)
{
perror("Error ");
printf("Press any key to exit...\n");
exit(EXIT_FAILURE);
}
ft = fopen(file3, "w"); // Opening in write mode
if(ft == NULL)
{
perror("Error ");
printf("Press any key to exit...\n");
exit(EXIT_FAILURE);
}
while((ch = fgetc(fs1)) != EOF)
fputc(ch,ft);
while((ch = fgetc(fs2)) != EOF)
fputc(ch,ft);
printf("The two files were merged into %s file successfully.\n", file3);
fclose(fs1);
fclose(fs2);
fclose(ft);
return 0;
}
my read.c - to read files
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
char c[1000];
FILE *fptr, anotherfptr;
if ((fptr = fopen("myfile1.txt", "r")) == NULL) {
printf("Error! opening file");
exit(1);
}
// reads text until newline
fscanf(fptr,"%[^\n]", c);
printf("Data from the file:\n%s", c);
fclose(fptr);
if ((fptr = fopen("myfile2.txt", "r")) == NULL) {
printf("Error! opening file");
exit(1);
}
// reads text until newline
fscanf(anotherfptr,"%[^\n]", c);
printf("Data from the file:\n%s", c);
fclose(anotherfptr);
return 0;
}
My issue is my logic on how to solve this simple program. I am literally stuck.
Any help/clarification would be much appreciated.

Answer 1

In this case you need to create a program which should know the content/size of 'myfile1.txt' or 'myfile2.txt' so as to show * for the second content while reading 'myfile3.txt'.
I prefer not to create separate c programs for each task but to use it as a function in one single program.
Coming to the logic : Masking is what you are searching for. Basically it is used as a password masking. ( You might have seen * while typing password in any sites. ). In your case you want to display a content as * without actually changing the content in file.
Get an idea of how masking is done for password in the below document :
https://www.geeksforgeeks.org/print-in-place-of-characters-for-reading-passwords-in-c/

Answer 2

Hope you have tried all possible way out. Please check the solution below :
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
char c1[1000];
char c3[1000];
FILE *fptr, *anotherfptr;
if ((fptr = fopen("myfile1.txt", "r")) == NULL) {
printf("Error! opening file");
exit(1);
}
// reads text until newline
fscanf(fptr,"%[^\n]", c1);
printf("Data from the file myfile1.txt :%s\n", c1);
fclose(fptr);
//calculate the length of string c1
int lengthc1=strlen(c1);
printf("Length of string c1 is : %d\n", lengthc1);
if ((anotherfptr = fopen("myfile3.txt", "r")) == NULL) {
printf("Error! opening file");
exit(1);
}
// reads text until newline
fscanf(anotherfptr,"%[^\n]", c3);
printf("Data from the file myfile3.txt :%s\n", c3);
fclose(anotherfptr);
//to show data of myfile2.txt in astrisk
int lengthc3=strlen(c3);
printf("Final data is ");
for ( int i=0 ; i<=lengthc3 ; i++)
{
if (i < lengthc1)
{
printf("%c", c3[i]);
}
else
{
printf("*");
}
}
return 0;
}