Problem reading a file

**caduardo21** · 04-18-2005

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void remover_newline(char *);

struct dados {
	char matricula[5];
	char nome[40];
	char curso[20];
	char nota[2];
} aluno;

int main(void)
{
	char linha[40];
	FILE *dados;
	
	
	
	dados = fopen("dados.txt", "r");
	if(dados == NULL){
		printf("dados.txt - arquivo desconhecido\n");
		getchar();
		exit(1);
	}

	while(fgets(linha, sizeof(linha), dados) != NULL){
		
		remover_newline(linha);
		strcpy(aluno.matricula, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.nome, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.curso, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.nota, linha);

		printf("aluno.matricula: %s\n", aluno.matricula);
		printf("aluno.nome: %s\n", aluno.nome);
		printf("aluno.curso: %s\n", aluno.curso);
		printf("aluno.nota: %s\n\n", aluno.nota);

		break;
	}

	fclose(dados);

	return 0;
}

void remover_newline(char *linha)
{
	char *ptr;

	ptr = strchr(linha, '\n');
	if(ptr != NULL)
		*ptr = '\0';
}

dados.txt:

Code:

20457
Denis Rocha da Silva
Linguagem de programação
{5} {40} {20} {2}

98364
Tom Hanks
Teatro
{38} {42} {2} {27}

44078
Nicolas Cage
História
{11} {29} {5} {37}

10904
Sabrina da Silva Sauro
Matemática
{3} {43} {11} {18}

12003
Charles Petzold
Programação
{34} {23} {12} {1}

The output:

Code:

aluno.matricula: 20457Denis Rocha da Silva
aluno.nome: Denis Rocha da Silva
aluno.curso: Linguagem de program{5} {40} {20} {2}
aluno.nota: {5} {40} {20} {2}

I've been trying to fix this for a long time and it is driving me crazy. What am I doing wrong? I also have this strange feeling that there is a better way to do this. Help please.

**itsme86** · 04-18-2005

I'm not so great at portuguese. What are you expecting from your program that isn't happening?

EDIT: Oh well. One thing I notice is that you're not allocating enough space for your strings:

Code:

	char matricula[5];
        char curso[20]
	char nota[2];

The string you're storing in matricula is 6 characters, but you're only allowing for 5. Don't forget about the '\0' at the end of the string. Same with curso.

And nota, well, that string is definitely a lot longer than 2 characters.

**Dave_Sinkula** · 04-18-2005

Code:

struct dados {
	char matricula[5];
	char nome[40];
	char curso[20];
	char nota[2];
} aluno;

Make enough space for the text and trailing null.

Code:

20457
Denis Rocha da Silva
Linguagem de programação
{5} {40} {20} {2}

[edit]Why have a loop that always breaks in the first pass?

**itsme86** · 04-18-2005

Geez, Dave. Give a guy enough time to edit his post will ya?

**caduardo21** · 04-18-2005

That was lame

Thanks.

As for the break, I was trying to get it right first, that is why I used it.

**caduardo21** · 04-18-2005

I'm confused now...

Why does char nota[2] works with let's say numbers 34, 23, 54, 2 and char matricula[5] doesn't work with numbers like 12345, 74957, 35409?

**Salem** · 04-18-2005

> Why does char nota[2] works with let's say numbers 34, 23, 54, 2
That would be down to "luck".

The character arrays inside your struct may (or may not) be padded with spare bytes. So whilst you can apparently use these and have a "working" program, it still doesn't mean that its correct code.

Change your compiler or your struct, and it will just stop "working" for no readily apparent reason.

**caduardo21** · 04-18-2005

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void remover_newline(char *);

struct dados {
	char matricula[6]; /* 1 a mais por causa do \0 no final */
	char nome[41];     /* mesma coisa... */
	char curso[21];    /* mesma coisa... */
	char nota[3];      /* mesma coisa... */
} aluno;

int main(void)
{
	char linha[40];
	FILE *dados;
	
	
	
	dados = fopen("dados.txt", "r");
	if(dados == NULL){
		printf("dados.txt - arquivo desconhecido\n");
		getchar();
		exit(1);
	}

	while(fgets(linha, sizeof(linha), dados) != NULL){
		
		remover_newline(linha);
		strcpy(aluno.matricula, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.nome, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.curso, linha);

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.nota, linha);

		printf("aluno.matricula: %s\n", aluno.matricula);
		printf("aluno.nome: %s\n", aluno.nome);
		printf("aluno.curso: %s\n", aluno.curso);
		printf("aluno.nota: %s\n\n", aluno.nota);

		/* pula a linha em branco */
		fgets(linha, sizeof(linha), dados);
	}

	fclose(dados);

	return 0;
}

void remover_newline(char *linha)
{
	char *ptr;

	ptr = strchr(linha, '\n');
	if(ptr != NULL)
		*ptr = '\0';
}

dados.txt:

Code:

20451
Denis Rocha da Silva
Arquitetura Arquiter
5

98364
Tom Hanks
Teatro
38

44076
Nicolas Cage
Futebol
44

10902
Sabrina da Silva Sauro
Basquete
3

12008
Charles Petzold
Tiro ao alvo
12

So, is this correct now?

**itsme86** · 04-18-2005

I'm assuming you changed the data line for nota? There's a fundamental flaw in your program and if you fixed it, you wouldn't have to worry about any buffer overflow problems. Look at how you're reading in a line:

Code:

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strcpy(aluno.nome, linha);

The use of linha is problematic because linha is bigger than your smallest struct member. I'd go with one of three options to fix it:
1) Forget linha...get rid of it. Make your struct members 1 element bigger than you're ultimately going to need. Then you can just read in a line like so:

Code:

		fgets(aluno.nome, sizeof(aluno.nome), dados);
		remover_newline(aluno.nome);

2) Make sure linha is at least one bigger than the largest struct member and then use the size of the struct member as the second argument to fgets(). Something like:

Code:

		fgets(linha, sizeof(aluno.nome)+1, dados);
		remover_newline(linha);
		strcpy(aluno.nome, linha); // If remover_newline() didn't remove a newline it will still overflow.

3) Use strncpy() instead of strcpy():

Code:

		fgets(linha, sizeof(linha), dados);
		remover_newline(linha);
		strncpy(aluno.nome, linha, sizeof(aluno.nome));
                aluno.nome[sizeof(aluno.nome)-1] = '\0';

Personally, I'd probably go with option 3.

Thread: Problem reading a file

Thread Tools

Search Thread

Display

Problem reading a file

Similar Threads

File transfer- the file sometimes not full transferred

Post...

Problem reading data from file and record it for use in program

airport Log program using 3D linked List : problem reading from file

Problem reading file