problems with writing a file in C in a Linux environment - c

Question

I'm trying to build a gym program for a project in college.
We're doing it in C in a Linux environment.
I do not have problems reading from the file, but when I try to update the file, if I print to file with '\n' at the end, it puts double enters between line. And if I don't, it puts all the data in one line.
What should I do?
i.e. I've added an example of a function that reads from the file and one that updates it.
Employees** Init_Gym_emp(Employees** emp, int* num) {
FILE* f = fopen("Gym Employees.txt", "r");
if (f == NULL) {
printf("Failed opening the file. Exiting!\n");
exit(1);
}
char c = '\0';
while (fscanf(f, "%c", &c) == 1) {
if (c == '\n') num[0]++;
}
if (num[0] > 0) num[0]++;
fseek(f, 0, SEEK_SET);
Employees* tmp = (Employees*)malloc(sizeof(Employees));
if (tmp == NULL) {
printf("Memory allocation failed\n");
exit(1);
}
emp = (Employees**)malloc(sizeof(Employees*)*(num[0]));
if (emp == NULL) {
printf("Memory allocation failed\n");
exit(1);
}
int i = 0;
tmp->first_name = (char*)malloc(sizeof(char)* 20);
tmp->last_name = (char*)malloc(sizeof(char)* 20);
tmp->user_name = (char*)malloc(sizeof(char)* 20);
tmp->password = (char*)malloc(sizeof(char)* 20);
tmp->user_type = (char*)malloc(sizeof(char)* 20);
while (fscanf(f, "%20[^#]%*c%20[^#]%*c%ld%*c%20[^#]%*c%10[^#]%*c%20[^#]%*2c", tmp->first_name, tmp->last_name, &tmp->id, tmp->user_name, tmp->password, tmp->user_type) == 6) {
emp[i] = (Employees*)malloc(sizeof(Employees));
if (emp[i] == NULL) {
printf("Memory allocation failed\n");
exit(1);
}
emp[i]->first_name = (char*)malloc(sizeof(char)* (strlen(tmp->first_name) + 1));
emp[i]->last_name = (char*)malloc(sizeof(char)* (strlen(tmp->last_name) + 1));
emp[i]->user_name = (char*)malloc(sizeof(char)* (strlen(tmp->user_name) + 1));
emp[i]->password = (char*)malloc(sizeof(char)* (strlen(tmp->password) + 1));
emp[i]->user_type = (char*)malloc(sizeof(char)* (strlen(tmp->user_type) + 1));
strcpy(emp[i]->first_name, tmp->first_name);
strcpy(emp[i]->last_name, tmp->last_name);
strcpy(emp[i]->user_name, tmp->user_name);
strcpy(emp[i]->password, tmp->password);
strcpy(emp[i]->user_type, tmp->user_type);
emp[i]->id = tmp->id;
i++;
}
free(tmp->first_name);
free(tmp->last_name);
free(tmp->user_name);
free(tmp->password);
free(tmp->user_type);
free(tmp);
fclose(f);
return emp;
}
void update_Gym_emp(Employees** emp, int* num) {
remove("Gym Employees.txt");
FILE* f = fopen("Gym Employees.txt", "w");
if (f == NULL) {
printf("Failed opening the file. Exiting!\n");
exit(1);
}
int i;
for (i = 0; i < num[0]; i++) {
fprintf(f, "%s#%s#%ld#%s#%s#%s#", emp[i]->first_name, emp[i]->last_name, emp[i]->id, emp[i]->user_name, emp[i]->password, emp[i]->user_type);
}
fclose(f);
}

Answer 1

here is one way the code could be written.
Notice that the first function reads from a file and creates a 2D list of Employee records
Notice that the second function writes to that same file from the 2D list of Employee records
Notice the string lengths for the call to fscanf() are one less than the related input buffer size because when scanning a string, the function will always append a NUL byte to the string
Strongly suggest defining the Employee struct as follows rather than the way it is currently defined:
struct Employee
{
char first_name[20];
char last_name[20];
long id;
char user_name[20];
char password[10];
char user_type[20];
};
Now, the proposed code
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Employee
{
char *first_name;
char *last_name;
long id;
char *user_name;
char *password;
char *user_type;
};
typedef struct Employee Employees;
// prototypes
void cleanup( Employees **emp );
Employees** Init_Gym_emp(Employees** emp, int* num)
{
FILE* f = fopen("Gym Employees.txt", "r");
if (f == NULL)
{
perror("fopen for Gym Employees.txt for input failed");
exit(1);
}
// implied else, fopen successful
char buffer[1024]; // input work area
// get count of records in file
while ( fgets(buffer, sizeof(buffer), f) )
{
num[0]++;
}
// step back to beginning of file to read/parse each record
if( fseek(f, 0, SEEK_SET) )
{ // then fseek failed
perror( "fseek to start of file failed" );
fclose( f );
exit( EXIT_FAILURE );
}
// implied else, fseek successful
// allocate array of pointers large enough for all records in input file
if( NULL == (*emp = malloc((size_t)num[0] * sizeof(Employees*) ) ) )
{
perror("malloc for array of pointers to Employee records failed");
cleanup( emp );
fclose( f );
exit(1);
}
// clear all pointers to NULL, to make cleanup easier
memset( *emp, '\0', (size_t)num[0] * sizeof( Employees* ));
char first_name[20];
char last_name[20];
long id;
char user_name[20];
char password[10];
char user_type[20];
int i = 0;
while( i < num[0] && fgets( buffer, sizeof(buffer), f ) )
{
if( 6 != sscanf(buffer,
"%19[^#]# %19[^#]# %ld# %19[^#]# %9[^#]# %19[^#]",
first_name,
last_name,
&id,
user_name,
password,
user_type) )
{ // then sscanf failed
perror( "sscanf for fields of emp record failed" );
cleanup( emp );
fclose( f );
exit( EXIT_FAILURE );
}
// implied else, sscanf successful
// get room for one employee record
if( NULL == (emp[i] = malloc(sizeof(Employees)) ) )
{
perror("malloc for new employee record failed");
cleanup( emp );
fclose( f );
exit( EXIT_FAILURE );
}
// implied else, malloc successful
(*emp)[i].first_name = strdup( first_name );
(*emp)[i].last_name = strdup( last_name );
(*emp)[i].user_name = strdup( user_name );
(*emp)[i].password = strdup( password );
(*emp)[i].user_type = strdup( user_type );
(*emp)[i].id = id;
i++;
} // end while
fclose(f);
return emp;
} // end function: Init_Gym_emp
void update_Gym_emp(Employees** emp, int* num)
{
FILE* f = fopen("Gym Employees.txt", "w");
if (f == NULL)
{
perror("fopen for Gym Employees.txt for write failed");
cleanup( emp );
exit(1);
}
// implied else, fopen successful
for (int i = 0; i < num[0]; i++)
{
fprintf(f, "%s#%s#%ld#%s#%s#%s#",
(*emp)[i].first_name,
(*emp)[i].last_name,
(*emp)[i].id,
(*emp)[i].user_name,
(*emp)[i].password,
(*emp)[i].user_type);
}
fclose(f);
} // end function: update_Gym_emp