C language reading from file and placing in variables - c

Question

In a text file I have the form Type:Username Password, how do I place it in three different variables, so that the variable Type is in the variable type, username is in username, and password is in password in C ?
Example:
Admin:Username Password
How to make?
Type:Admin
User:Username
Pw:Password
Here's my code:
int ch;
int i = 0;
while ((ch = fgetc(fp)) != EOF) {
// Check for the colon character
if (ch == ':') {
// We have reached the end of the type string
// Move to the next variable
i = 0;
continue;
}
// Check for the space character
if (ch == ' ')
{
// We have reached the end of the username string
// Move to the next variable
i = 0;
continue;
}
// Store the character in the appropriate variable
if (i < 50) {
if (type[0] == 0) {
type[i] = ch;
} else if (username[0] == 0) {
username[i] = ch;
} else {
password[i] = ch;
}
i++;
}
}

Answer 1

Considering your initial requirement that you posted in your Question, that a text file consists of following line:
Admin:Username Password
To store Admin in variable type, Username in variable username and similarly Password in variable Password.
You can declare a structure something similar to:
typedef struct user {
char type[512];
char username[512];
char password[512];
} user;
And as #IngoLeonhardt commented, that strtok() or strchr() can be used to parse the line read from the text file, you can refer the below simple example code snippet to understand and further improve the logic.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct user {
char type[512];
char username[512];
char password[512];
} user;
int main(void)
{
FILE *file = fopen("test.txt","r");
char *line = NULL;
size_t linesize = 0;
char *token;
const char colon[2] = ":";
const char space[2] = " ";
user user_1;
if (file)
{
while (getline(&line, &linesize, file) != -1)
{
printf("%s\n", line);
token = strtok(line, colon);
strcpy(user_1.type, token);
token = strtok(NULL, space);
strcpy(user_1.username, token);
token = strtok(NULL, space);
strcpy(user_1.password, token);
printf("%s\n", user_1.type);
printf("%s\n", user_1.username);
printf("%s", user_1.password);
free(line);
}
fclose(file);
}
return 0;
}
PS: There may be some flaws/bugs in above implementation, please consider the above code just as an example.

Answer 2

Here is a solution which reads one character at a time from the file:
#include <stdio.h>
#include <stdlib.h>
#define MAX_STRING_SIZE 200
int main( void )
{
char type[MAX_STRING_SIZE];
char user[MAX_STRING_SIZE];
char pw[MAX_STRING_SIZE];
FILE *fp;
int ch;
int i;
//open the input file
fp = fopen( "input.txt", "r" );
if ( fp == NULL )
{
fprintf( stderr, "Error opening file!\n" );
exit( EXIT_FAILURE );
}
//read first token
i = 0;
while ( ( ch = fgetc( fp ) ) != ':' )
{
if ( ch == EOF )
{
fprintf( stderr, "Input error!\n" );
exit( EXIT_FAILURE );
}
if ( i == MAX_STRING_SIZE )
{
fprintf( stderr, "Sub-string is too long!\n" );
exit( EXIT_FAILURE );
}
type[i++] = ch;
}
type[i] = '\0';
//read second token
i = 0;
while ( ( ch = fgetc( fp ) ) != ' ' )
{
if ( ch == EOF )
{
fprintf( stderr, "Input error!\n" );
exit( EXIT_FAILURE );
}
if ( i == MAX_STRING_SIZE )
{
fprintf( stderr, "Sub-string is too long!\n" );
exit( EXIT_FAILURE );
}
user[i++] = ch;
}
user[i] = '\0';
//read third token
i = 0;
while ( ( ch = fgetc( fp ) ) != EOF )
{
if ( i == MAX_STRING_SIZE )
{
fprintf( stderr, "Sub-string is too long!\n" );
exit( EXIT_FAILURE );
}
pw[i++] = ch;
}
pw[i] = '\0';
//close the file
fclose( fp );
//print the three strings
printf( "Type:%s\n", type );
printf( "User:%s\n", user );
printf( "Pw:%s\n", pw );
}
For the input stated in the question, this program has the desired output:
Type:Admin
User:Username
Pw:Password
Here is an alternative solution, which reads a whole line at once:
This solution reads a line from the file as a string, by using the function fgets. After doing that, it uses the function strchr to find the ':' and ' ' delimiter characters in the string. Once they are found, the characters between the tokens can be copied so that they form a string.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define MAX_STRING_SIZE 200
bool read_exactly_one_line( char buffer[], int buffer_size, FILE *fp );
int main( void )
{
char type[MAX_STRING_SIZE];
char user[MAX_STRING_SIZE];
char pw[MAX_STRING_SIZE];
FILE *fp;
char line[500];
char *p, *q;
int token_length;
//open the input file
fp = fopen( "input.txt", "r" );
if ( fp == NULL )
{
fprintf( stderr, "Error opening file!\n" );
exit( EXIT_FAILURE );
}
//read one line of input
if ( ! read_exactly_one_line( line, sizeof line, fp ) )
{
fprintf( stderr, "File is empty!\n" );
exit( EXIT_FAILURE );
}
//find the delimiter between the first and second token
p = strchr( line, ':' );
if ( p == NULL )
{
fprintf( stderr, "Unable to find first delimiter!\n" );
exit( EXIT_FAILURE );
}
//verify that first token is not too large
token_length = p - line;
if ( token_length >= MAX_STRING_SIZE )
{
fprintf( stderr, "Token too large!\n" );
exit( EXIT_FAILURE );
}
//copy the first token
memcpy( type, line, token_length );
type[token_length] = '\0';
//move pointer to start of second token
p++;
//find the delimiter between the second and third token
q = strchr( p, ' ' );
if ( q == NULL )
{
fprintf( stderr, "Unable to find second delimiter!\n" );
exit( EXIT_FAILURE );
}
//verify that second token is not too large
token_length = q - p;
if ( token_length >= MAX_STRING_SIZE )
{
fprintf( stderr, "Token too large!\n" );
exit( EXIT_FAILURE );
}
//copy the second token
memcpy( user, p, token_length );
user[token_length] = '\0';
//move pointer to start of third token
q++;
//verify that third token is not too large
token_length = strlen( q );
if ( token_length >= MAX_STRING_SIZE )
{
fprintf( stderr, "Token too large!\n" );
exit( EXIT_FAILURE );
}
//copy the third token
memcpy( pw, q, token_length );
pw[token_length] = '\0';
//close the file
fclose( fp );
//print the three strings
printf( "Type:%s\n", type );
printf( "User:%s\n", user );
printf( "Pw:%s\n", pw );
}
//This function will read exactly one line and remove the newline
//character, if it exists. On success, it will return true. If this
//function is unable to read any further lines due to end-of-file,
//it returns false. If it fails for any other reason, it will not
//return, but will print an error message and call "exit" instead.
bool read_exactly_one_line( char buffer[], int buffer_size, FILE *fp )
{
char *p;
//attempt to read one line from the stream
if ( fgets( buffer, buffer_size, fp ) == NULL )
{
if ( ferror( fp ) )
{
fprintf( stderr, "Input error!\n" );
exit( EXIT_FAILURE );
}
return false;
}
//make sure that line was not too long for input buffer
p = strchr( buffer, '\n' );
if ( p == NULL )
{
//a missing newline character is ok if the next
//character is a newline character or if we have
//reached end-of-file (for example if the input is
//being piped from a file or if the user enters
//end-of-file in the terminal itself)
if ( getc(fp) != '\n' && !feof(stdin) )
{
printf( "Line input was too long!\n" );
exit( EXIT_FAILURE );
}
}
else
{
//remove newline character by overwriting it with a null
//character
*p = '\0';
}
return true;
}
This program has the same output as the first one.