Thread: fprintf doesn't write to file anymore

I'am building a program that creates files with input from user using structs. I'am having problem with doing that right.
I don't understand what the problem is, it was working fine sometime ago then i decided to try new things and all of a sudden it stopped working. Right now i'am just focusing on function Adicionar(), it should printf to the file the data that the user gives.

Code:

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


void Menu(FILE *f);


typedef struct
{
    int numTeste;
    float nota;
    char descricao[50]; 
    
}Aluno;


void Listar(FILE *f)
{


}


void Adicionar(FILE *f)
{
    int N;
    printf("Quantos testes deseja inserir?");
    scanf("%d", &N);
    Aluno novoAluno[N];
    for(int i=0;i<N;i++)
    {
        printf("Insira o numero do teste: ");
        scanf("%d", &novoAluno[i].numTeste);
        printf("%d", novoAluno[i].numTeste);
        fprintf(f, "%d\n", novoAluno[i].numTeste);
        printf("Insira a nota: ");
        scanf("%f", &novoAluno[i].nota);
        printf("%.2f", novoAluno[i].nota);
        fprintf(f, "%.2f\n", novoAluno[i].nota);
        printf("Insira detalhes(pratica, teoria...): ");
        scanf("%s", novoAluno[i].descricao);
        fprintf(f, "%s\n", novoAluno[i].descricao);
    }
    printf("\n");
    printf("Todos os dados relativos aos testes foram inseridos.\n");
    printf("****************************************************\n");
    Menu(f);
    
    
}


void Editar()
{
    
    
}


void Remover()
{
    
}


void Menu(FILE *f)
{
    int opcao;
    
    printf("   Menu\n\n");
    printf("1 --> Listar\n");
    printf("2 --> Adicionar\n");
    printf("3 --> Editar\n");
    printf("4 --> Remover\n");
    printf("5 --> Sair\n");
    scanf(" %d", &opcao);
        
    switch(opcao)
    {
        case 1: Listar(f);break;
        case 2: Adicionar(f);break;
        case 3: Editar();break;
        case 4: Remover();break;
        case 5: printf("A fechar o programa!\n"); break;
        default : printf("Opcao invalida!\n"); break;
            
    }    
        


}






int main()
{
    
    
    char nomeFicheiro[50];
    printf("Qual o nome do ficheiro a criar? ");
    scanf("%s", nomeFicheiro);
    char auxFicheiro[50];
    sprintf(auxFicheiro, "%s.txt", nomeFicheiro);
    FILE *f;
    f=fopen(auxFicheiro, "w+");
    if(f==NULL)
    {
        printf("Erro\n");
        return 0;
    }    
    Menu(f);
    
}

Funny i wasn't doing the 5 to quit and that was the problem, now it works fine. I was just doing ctrl+c but i think before it worked with that but i'am not sure.

Then it's likely the output stream to the file was not being flushed in the current version of your code (but possibly was in the previous version). To test, flush the output in your loop, terminate the program with ctrl+c, and see if it works that time.

Code:

fflush(f);

However, you should let the program end naturally. This way, the file will be closed (which causes the output to be flushed) and everything should work without explicitly flushing it.

How do you suggest i do loop in main with Menu()?

Well, a good function should do one thing, and do it well. With that in mind, your "menu()" function is doing more than it should.

One approach might be as follows:

• Modify the "menu()" function so that it prints the menu, reads the input, and returns the input to "main()"
• In "main()", store the return value of "menu()" into a variable
• Use this returned value to determine what to do next (call another function, change the value of a flag, etc)
• Put the above two things into a loop, and use [an already mentioned] flag to determine whether to continue looping or not.

One doubt do i need return 0 in Adiciionar() or it's useless since it's a void function?

Returning zero would be wrong, since as you said, the function is declared with return type void.

Note, however, it is legal to return (with no value) from a void function. You normally do not need to explicitly return from a void function, but this can come in handy if you need to break out of a void function early.

Here's a contrived example:

Code:

void print_int_division(int dividend, int divisor)
{
    /* We cannot divide by zero, so exit the
       function  if "divisor" is zero */
    if(divisor == 0)
        return;  // void function, so we return, but do NOT return a value

    printf("%d / %d = %d\n",dividend,divisor,dividend/divisor);
}

Like this is good? I'am now working on Listar() function that has to printf the file to the screen. I think it's having problems reading from the file since the program is crashing when it calls this function. Why is this? Initially i had w+ which i didn't know erased he file if it exists so i changed to r+ but it's still crashing.

Code:

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


int Menu(FILE *f);


typedef struct
{
	int numTeste;
	float nota;
	char descricao[50]; 
	
}Aluno;


void Listar(FILE *f)
{
	int N;
	Aluno novoAluno[N];
	char st[10];
	N=0;
	while(fgets(st, 10, f)!=NULL)
	{
		novoAluno[N].numTeste=atoi(st);
		fgets(st, 10, f);
		novoAluno[N].nota=atof(st);
		fgets(novoAluno[N].descricao, 50, f);
		N++;
	}
	printf("Existem %d testes\n\n", N);
	int i;
	for(i=0;i<N;i++)
	{
		printf("Teste %d\n", novoAluno[i].numTeste);
		printf("Nota:  %.2f\n", novoAluno[i].nota);
		printf("Descricao: %s\n", novoAluno[i].descricao);
	}
	
}


void Adicionar(FILE *f)
{
	int N;
	printf("Quantos testes deseja inserir?");
	scanf("%d", &N);
	Aluno novoAluno[N];
	for(int i=0;i<N;i++)
	{
		printf("Insira o numero do teste: ");
		scanf("%d", &novoAluno[i].numTeste);
		printf("%d", novoAluno[i].numTeste);
		fprintf(f, "%d\n", novoAluno[i].numTeste);
		printf("Insira a nota: ");
		scanf("%f", &novoAluno[i].nota);
		printf("%.2f", novoAluno[i].nota);
		fprintf(f, "%.2f\n", novoAluno[i].nota);
		printf("Insira detalhes(pratica, teoria...): ");
		scanf("%s", novoAluno[i].descricao);
		fprintf(f, "%s\n", novoAluno[i].descricao);
	}
	fseek(f, 0, SEEK_SET);
	printf("\n");
	printf("Todos os dados relativos aos testes foram inseridos.\n");
	printf("****************************************************\n");
	
	
	
	
}


void Editar()
{
	
	
}


void Remover()
{
	
}


int Menu(FILE *f)
{
	int opcao;
	
	printf("   Menu\n\n");
	printf("1 --> Listar\n");
	printf("2 --> Adicionar\n");
	printf("3 --> Editar\n");
	printf("4 --> Remover\n");
	printf("5 --> Sair\n");
	scanf("%d", &opcao);
		
	switch(opcao)
	{
		case 1: Listar(f);break;
		case 2: Adicionar(f); break;
		case 3: Editar();break;
		case 4: Remover();break;
		case 5: printf("A fechar o programa!\n"); break;
		default : printf("Opcao invalida!\n"); break;
			
	}
	return opcao;	
}


int main()
{
	char nomeFicheiro[50];
	printf("Qual o nome do ficheiro a criar? ");
	scanf("%s", nomeFicheiro);
	char auxFicheiro[50];
	sprintf(auxFicheiro, "%s.txt", nomeFicheiro);
	FILE *f;
	f=fopen(auxFicheiro, "r+");
	if(f==NULL)
	{
		printf("Erro\n");
		return 0;
	}	
	int valorMenu;
	do
	{
		valorMenu=Menu(f);
	}while((valorMenu>=1)&&(valorMenu<=4));
	
	
	
	return 0;
}

Just realized what the problem was, i forgot to set the file position to the start of the file. With rewind(f) or fseek it works.