C coding - First number in text file not being read the way I expected

Question

I'm doing a function that consists of reading elements of a file I wrote and priting them. The problem is, it seems the first number for every line of the text file is being read and printed in a way I don't understand on how it arrived. It's mostly numbers from 90-110 and zeros.

I tried chaging the variable to chars and floats, but neither worked.

void imprimir_tabela(){
FILE *tabela = fopen("tabela.txt", "r");

if(tabela == NULL){
    printf("TABELA INVALIDA OU NAO ACHADA");
    printf("erro 404");
    exit(404);
}
int numero_atomico;
char abreviacao;
char nome[20];
float massa_atomica;
int grupo;
int periodo;

while(!feof(tabela))
{
fscanf(tabela, "%d %s %s %f %d %d", &numero_atomico, &abreviacao, &nome, &massa_atomica, &grupo, &periodo);
printf("%d - %s - %s - Massa atomica: %0.3f - Grupo: %d - Periodo: %d\n", numero_atomico, &abreviacao, &nome, massa_atomica, grupo, periodo);
}
rewind(tabela);
return 0;

Sample lines of the text file

1 H Hidrogenio 1.008 1 1
2 He Helio 4.003 18 1
3 Li Litio 6.941 1 2

The code, the result and the text file

Hello, welcome to StackOverflow. Please do not post images of your code. Instead, edit your question and add it as a formatted code block. — Janez Kuhar, Feb 27 '21 at 21:59
Post a sample line of input. Also do not call `printf()` with data from `scanf()` unless `scanf()` returns an expected value. — chux - Reinstate Monica, Feb 27 '21 at 22:10
See [Why is “while ( !feof (file) )” always wrong?](https://stackoverflow.com/q/5431941/2410359) — chux - Reinstate Monica, Feb 27 '21 at 22:10
Please copy the first couple of lines of the test file you are reading — Ed Heal, Feb 27 '21 at 22:12
`%s` reads a string `%c` reads a character.. Look at the 1nd `%s` if `fscanf` — Ed Heal, Feb 27 '21 at 22:15

Ed Heal · Answer 1 · 2021-02-27T22:33:38.083

See comments in the code below

void imprimir_tabela(){
FILE *tabela = fopen("tabela.txt", "r");

if(tabela == NULL){
    printf("TABELA INVALIDA OU NAO ACHADA");
    printf("erro 404");
    exit(404);
}
int numero_atomico;
char abreviacao;
char nome[20];
float massa_atomica;
int grupo;
int periodo;

do { // Use to be while(!feof(tabela)) - See link in the comments section
{
// 1 H Hidrogenio 1.008 1 1 
// For reference
// 1. Prevent buffer over run
// 3. record return value

int ret = fscanf(tabela, "%d %c %19s %f %d %d\n", &numero_atomico, &abreviacao, &nome, &massa_atomica, &grupo, &periodo);

switch (ret) {
  case 6: // Ok 
     printf("%d - %c - %s - Massa atomica: %0.3f - Grupo: %d - Periodo: %d\n", numero_atomico, abreviacao, &nome, massa_atomica, grupo, periodo);
     break;
  case EOF: // End of file - we are done
     break:
  default:
     // Report error - take some action - in this case exit
     fprintf(stderr, "Error in file %s\n", "tabela.txt");
     exit(-1);
// Are we done    
} while (ret != EOF);

// rewind(tabela); - Not required
// But this is
fclose(tabela);
return 0;
}

And please fix the indentation - I leave that as an exercise to the reader

NMDV, 1) OP has posted sample input. like "3 Li Litio 6.941 1 2" which fails to scan here. — chux - Reinstate Monica, Feb 27 '21 at 22:32
Huh sorry to ask something more even though you gave a lot of info, but what does %19s do? — CARLOS EDUARDO NISHI, Feb 27 '21 at 23:33
Please read the manual page for `scanf` - it reads at most 19 characters. Your array is 20 characters. You need the extra one for the null character — Ed Heal, Feb 27 '21 at 23:36

chux - Reinstate Monica · Accepted Answer · 2021-02-27T22:25:29.320

-1

At least this problem: reading into char as if it was enough for a string.

char abreviacao;

//                    vv --- needs more meory than 1 `char`
fscanf(tabela, "%d %s %s %f %d %d", 
    &numero_atomico, &abreviacao, &nome, &massa_atomica, &grupo, &periodo);

Same problem with printf()

Also

Limit input width of string
check the return value of scanf().

int numero_atomico;
//char abreviacao;
char abreviacao[4];  // Some elements need 3 letters.
char nome[20];
float massa_atomica;
int grupo;
int periodo;

// while(!feof(tabela))
while(fscanf(tabela, "%d %3s %19s %f %d %d", 
    &numero_atomico, abreviacao, nome, &massa_atomica, &grupo, &periodo) == 6) {
  printf("%d - %s - %s - Massa atomica: %0.3f - Grupo: %d - Periodo: %d\n", 
      numero_atomico, &abreviacao, &nome, massa_atomica, grupo, periodo);
}
// rewind(tabela); // not needed

Recommend also to use double massa_atomica.

edited Feb 27 '21 at 22:25

answered Feb 27 '21 at 22:14

chux - Reinstate Monica

143,097
13
135
256

@EdHeal Feel feel to add your insights here (its wiki) or post an answer. – chux - Reinstate Monica Feb 27 '21 at 22:17
Oh god, I'm in pain, I just changed it to char abreviacao[3] and it works now. – CARLOS EDUARDO NISHI Feb 27 '21 at 22:18
See comments below the question – Ed Heal Feb 27 '21 at 22:19
@CARLOSEDUARDONISHI Without posting sample data, I suspect you will have additional issues. – chux - Reinstate Monica Feb 27 '21 at 22:19
Sorry, first time using the website, lesson learned! – CARLOS EDUARDO NISHI Feb 27 '21 at 22:21
[Placeholder names](https://www.thoughtco.com/element-symbols-not-in-use-606524#:~:text=Placeholder%20names%20basically%20express%20the,new%20name%20and%20element%20symbol.) – chux - Reinstate Monica Feb 27 '21 at 22:28

C coding - First number in text file not being read the way I expected

2 Answers2