Getting values from a mixed string

Question

I am trying to get the values I need from a string using sscanf, but I can't get it done. Here is what I am trying to do:

I have a string which has this pattern

2 7 A BUL

(integer space integer space character space string of 3 elements)

I have to get each value separated by spaces and store it into variables.

This is my code:

sscanf(string[i],"%d %d %s %s",&e,&m,id,modelo);

The problem I'm having is that it only stores the first integers, ignoring the chars.

How can I fix this?

Thank you.

EDIT:

Here's the whole code for the function:

void le_lista(lista *l) {
int e,m;
char id[1],modelo[3],frase[20][12];
int linha=0;
while (1) {
    fgets(frase[linha],12,stdin);
    //

    if (feof(stdin)) {
        break;
    }
    //
    linha++;
}
int i;
for(i=0;i<=linha;i++) {
    sscanf(frase[i],"%d %d %s %s",&e,&m,&id,&modelo);
    enfila(e,m,id,modelo,l);
    //printf("%s",frase[i]);
}
printf("Linhas: %d",linha+1);
return;

}

Answer 1

char mystring[] = "2 7 A BUL"
x = strtok(mystring, " ");  //separates by spaces

More here Split string with delimiters in C

Answer 2

Given that you want to recognize 2 7 A BUL, you cannot safely use:

int e,m;
char id[1], modelo[3];

sscanf(frase[i], "%d %d %s %s", &e, &m, &id, &modelo);

First, you shouldn't pass char (*)[] values where a char * is expected; do not take the address of an array; pass id and modelo only. GCC will warn you about that if you turn on warnings. If you're learning C, you can't afford not to have the warnings turned on (use -Wall at minimum; -Wall -Wextra if at all possible).

Next, the first %s will read an arbitrary number of characters and null-terminate the result. This is going to overwrite the end of the id array. And you can't safely read 3 characters into modelo either. Because of this, you have two stack overflow problems.

You should write either:

int e, m;
char id[2], modelo[4];

if (sscanf(frase[i], "%d %d %1s %3s", &e, &m, id, modelo) != 4)
    ...oops...

or perhaps:

int e, m;
char id;
char modelo[4];

if (sscanf(frase[i], "%d %d %c %3s", &e, &m, &id, modelo) != 4)
    ...oops...

Or, you could use char id[1]; and %c, but that is dangerous; the result is not a null-terminated string.

Your primary input loop is suspect too. You can use feof() as you did, immediately after the fgets(), but it is much more conventional to test the result of fgets() itself; it tells you whether it succeeded or not. That code should probably be:

char frase[20][12];

for (int linha = 0; i < sizeof(frase) / sizeof(frase[0]); i++)
{
    if (fgets(frase[linha] ,sizeof(frase[linha]), stdin) == 0)
        break;
}

This avoids repeating the 20 or the 12 but protects you from too many lines. It does not protect you from overlong lines; you could add:

size_t len = strlen(frase[linha]);
assert(len != 0);
if (frase[len-1] != '\n')
    ...input was too long...

to the loop.

You could also think about doing the sscanf() and call to enfila() in the main input loop; you would not then need the frase array to be multi-dimensional.

---

Putting all the changes together:

char frase[4096];

while (fgets(frase, sizeof(frase), stdin) != 0)
{
    int e;
    int m;
    char id[2];
    char modelo[4];
    if (sscanf(frase, "%d %d %1s %3s", &e, &m, id, modelo) == 4)
        enfila(e, m, id, modelo, l);  // l is the parameter to the function
    else
        ...report error...
}

Using fgets() and sscanf() was definitely the correct way to go. It means that error reporting can show the whole line of input, rather than whatever mangled remains scanf() left behind as unreadable.

Answer 3

use instead strtok which is more simpler and IMHO more solid since you can do a simple add error handling

e.g.

int j = 0;
for (char* token = strtok(frase[i]," "; token != NULL; token = strtok(NULL," ")
{
  switch(j++)
  {
    case 0: 
      e = atoi(token); 
      break;
    case 1: 
      m = atoi(token); 
      break;
    case 2: 
      strncpy(id,token,sizeof(id)); // or strcpy_s
      break;
    case 3: 
      strncpy(modelo,token,sizeof(modelo));  // or strcpy_s
      break;
    default: 
      printf( "invalid number of arguments in line %d\n", i ); 
      break;
  }
}