Programming Forums > Application Development > C++

Spaam · Oct 19th, 2004, 12:04 AM

I am trying to read a text file into a structure of arrays. Every second line should go into different members of the structure, name and number. However, as soon as I try to assign a value to any member, I get a segmentation error.

Strangely I can get this to work using only ONE member, it's when I use two it stops working.

Second question. At first I tried declaring the structure members as "char name[]" and "char name[100]" but this didn't work. For some reason I CAN however treat these char pointers as if they were arrays, which they are not (if I use only one...) how come?

Any input into as to why I get a segmentation error or general tips as to how I might better be able to solve this problem would be greatly appreciated. I am at a total loss. Thanks.

ps. this function is part of a bigger program. Obviously the function is pointless as it is, I just need to get this thing working before I can write anything else.
It gets called as as follows:
"read_file(&fp, dbcontacts);"
fp being a file pointer and dbcontacts the structure

Code follows:

#include <stdio.h>
#define TRUE 1
#define FALSE 0
#define MAX 200

typedef struct {
char *name;
char *number;
} database;

void read_file(FILE *fp, database dbcontacts[]) {
int c, t_names=0, t_chars=0, read_name=TRUE, t_numbers=0, t_digits=0;

while ((c = getc(fp)) != EOF) {
printf("\ndata: %s", dbcontacts[0].name);
if (read_name == FALSE && c != '\n') {
dbcontacts[t_numbers].number[t_digits] = c;
t_digits++;
}
if (read_name == FALSE && c == '\n') {
dbcontacts[t_numbers].number[t_digits] = '\0';
t_digits = 0;
t_numbers++;
read_name = TRUE;
}
if (read_name == TRUE && c != '\n') {
dbcontacts[t_names].name[t_chars] = c;
t_chars++;
}
if (read_name == TRUE && c == '\n') {
dbcontacts[t_names].name[t_chars] = '\0';
t_chars = 0;
t_names++;
read_name = FALSE;
}
}

printf("\n");
return;
}

Daggerhex_Flynn · Oct 19th, 2004, 3:08 AM

You always have to show your datafile for IO questions, so I made an arbitrary example of a file with fixed width fields:

(Toggle Plain Text)

MakeSureTo 422
LeaveTwelve 433
SpacesFor  432
EachName  455
Field    663

(Toggle Plain Text)

#include<stdio.h>
#define SIZE 20
 
struct dataBase_t {
 char name [13];
 int number;
};
 
void readFile( FILE *, struct dataBase_t [] );
 
int main() {
 
 FILE *fptr = fopen("datafile","r");
 struct dataBase_t database[SIZE];
 
 readFile(fptr, database);
 fclose(fptr);
 
 return 0;
}
 
void readFile( FILE * fptr, struct dataBase_t database[] ) {
 char buffer[255];
 int i=0;
  
 for (i = 0; (fgets(buffer, 255, fptr)) != NULL && i < SIZE; ++i) {
  sscanf(buffer, "%12s%d",database[i].name, &database[i].number);
  
  printf("%s\n%d\n",database[i].name, database[i].number);
 }
}

mici · Oct 19th, 2004, 9:44 AM

Well as far as i can see your code lacks memory handling...
That is you've declared pointers in the struct... but you didn't give them room to fill.
use something like

dbcontacts[t_names].name =malloc(num_of_chars_max);

or if you need to modify size of theese memory arreas you can later us realloc();

or in the end just go C++ and use vectors.

Spaam · Oct 25th, 2004, 11:04 PM

Thanks a lot for the answers. Problem solved.

Oct 19th, 2004, 3:08 AM	#2
Daggerhex_Flynn Programmer Join Date: Oct 2004 Location: Canada Posts: 82 Rep Power: 5	You always have to show your datafile for IO questions, so I made an arbitrary example of a file with fixed width fields: (Toggle Plain Text) MakeSureTo 422 LeaveTwelve 433 SpacesFor 432 EachName 455 Field 663 MakeSureTo 422 LeaveTwelve 433 SpacesFor 432 EachName 455 Field 663 (Toggle Plain Text) #include<stdio.h> #define SIZE 20 struct dataBase_t { char name [13]; int number; }; void readFile( FILE , struct dataBase_t [] ); int main() { FILE fptr = fopen("datafile","r"); struct dataBase_t database[SIZE]; readFile(fptr, database); fclose(fptr); return 0; } void readFile( FILE * fptr, struct dataBase_t database[] ) { char buffer[255]; int i=0; for (i = 0; (fgets(buffer, 255, fptr)) != NULL && i < SIZE; ++i) { sscanf(buffer, "%12s%d",database[i].name, &database[i].number); printf("%s\n%d\n",database[i].name, database[i].number); } } #include<stdio.h> #define SIZE 20 struct dataBase_t { char name [13]; int number; }; void readFile( FILE , struct dataBase_t [] ); int main() { FILE fptr = fopen("datafile","r"); struct dataBase_t database[SIZE]; readFile(fptr, database); fclose(fptr); return 0; } void readFile( FILE * fptr, struct dataBase_t database[] ) { char buffer[255]; int i=0; for (i = 0; (fgets(buffer, 255, fptr)) != NULL && i < SIZE; ++i) { sscanf(buffer, "%12s%d",database[i].name, &database[i].number); printf("%s\n%d\n",database[i].name, database[i].number); } }

Oct 19th, 2004, 9:44 AM	#3
mici Programmer Join Date: Oct 2004 Posts: 67 Rep Power: 5	Well as far as i can see your code lacks memory handling... That is you've declared pointers in the struct... but you didn't give them room to fill. use something like dbcontacts[t_names].name =malloc(num_of_chars_max); or if you need to modify size of theese memory arreas you can later us realloc(); or in the end just go C++ and use vectors. __________________ coffee is my heroin.

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Oct 19th, 2004, 12:04 AM	#1
Spaam Newbie Join Date: Oct 2004 Posts: 2 Rep Power: 0	I am trying to read a text file into a structure of arrays. Every second line should go into different members of the structure, name and number. However, as soon as I try to assign a value to any member, I get a segmentation error. Strangely I can get this to work using only ONE member, it's when I use two it stops working. Second question. At first I tried declaring the structure members as "char name[]" and "char name[100]" but this didn't work. For some reason I CAN however treat these char pointers as if they were arrays, which they are not (if I use only one...) how come? Any input into as to why I get a segmentation error or general tips as to how I might better be able to solve this problem would be greatly appreciated. I am at a total loss. Thanks. ps. this function is part of a bigger program. Obviously the function is pointless as it is, I just need to get this thing working before I can write anything else. It gets called as as follows: "read_file(&fp, dbcontacts);" fp being a file pointer and dbcontacts the structure Code follows: #include <stdio.h> #define TRUE 1 #define FALSE 0 #define MAX 200 typedef struct { char name; char number; } database; void read_file(FILE *fp, database dbcontacts[]) { int c, t_names=0, t_chars=0, read_name=TRUE, t_numbers=0, t_digits=0; while ((c = getc(fp)) != EOF) { printf("\ndata: %s", dbcontacts[0].name); if (read_name == FALSE && c != '\n') { dbcontacts[t_numbers].number[t_digits] = c; t_digits++; } if (read_name == FALSE && c == '\n') { dbcontacts[t_numbers].number[t_digits] = '\0'; t_digits = 0; t_numbers++; read_name = TRUE; } if (read_name == TRUE && c != '\n') { dbcontacts[t_names].name[t_chars] = c; t_chars++; } if (read_name == TRUE && c == '\n') { dbcontacts[t_names].name[t_chars] = '\0'; t_chars = 0; t_names++; read_name = FALSE; } } printf("\n"); return; }

Oct 25th, 2004, 11:04 PM	#4
Spaam Newbie Join Date: Oct 2004 Posts: 2 Rep Power: 0	Thanks a lot for the answers. Problem solved.

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Programming Forums > Application Development > C++

Reading A Text File Into Structure [solved]