Sequence reading of space-separated numbers

Question

It is necessary to read only a line with a space-separated set of integers, each space-separated item will be inserted in a linked list: 1 41 2 15 6 7 87 4 2 1 9 0

List would be something like = [1, 41, 2, 15, 6, 7, 87, 4, 2, 1, 9, 0]

Example:

$ gcc example.c -o example -g -Wall 
$ ./example 
1 41 2 15 6 7 87 4 2 1 9 0<enter>

The biggest problem is that the amount of numbers that will come in the input is undefined, ie the input can also be: 1 8 6

Lista = [1, 8, 6]

Because the amount is undefined, I thought of two possible solutions:

• to) scanf ("%[^\n]%*c", sequenciaNumeros);
• b) Use fgets

In both cases, I would have to the problem of declaring a huge character vector to ensure it does not reach the limit.

If the quantity were set it would be simple:

scanf("%d %d %d, &valor1, &valor2, &valor3)

It is possible with the scanf take this line and be able to manipulate each of the numbers (which are separated by space) to add to the list, knowing the amount of numbers may vary? The input is only one row of a set of numbers separated by space

Answer 1

You can use the scanf(), for with it it is possible to distinguish the numbers between themselves.

To solve your problem, one possible way is read a number at a time and at each reading, dynamically allocate enough memory to read that number, using malloc(). For this you would need a structure that expands its size dynamically. This avoids the problem of:

1. Statically allocate too small a vector and fail to store all data.
2. Statically allocate a very large vector, wasting space in memory.

A data structure that assists you in this is a chain list. An alternative can be a dynamically sized array.

Either way you need to define an end identifier. Some character will dictate when the sequence ends. If it is a sequence of integer numbers, you can use a negative character to indicate the end of the sequence. For example, -1. Or EOF.

However, perhaps the following reflection should be made here: it is necessary for all the numbers to be in memory at once?

A very simple example to illustrate this scenario is a accumulator.

Setting: Imagine being asked a program to add up all the numbers the user enters.
Solution: One approach is to store everyone in memory and then iterate on them by adding them up. A simpler approach would be, just to make an accumulator:

soma = soma + numero_da_entrada;

I hope I’ve helped!

Issue 1: Apparently, you can use the return of scanf() to know when there are no more numbers to read:

int numero;
while(scanf("%d", &numero) == 1) { // scanf retorna 1 quando a leitura for bem sucedida
    printf("%d", numero);
}

Issue 2: To read the entire line and stop when press enter:

int numero;
char proxChar;
while(scanf("%d%c", &numero, &proxChar) == 2) { 
        printf("%d", numero);
        if(proxChar == '\n') break; 
}

Answer 2

Read only one number at a time. The result of scanf will then be 1 if reading was successful, or zero if failed, and in this case the line was read completely.

For each number read, allocate space dynamically with malloc. Use a chained list to store read numbers.

Answer 3

You can use the fgets to take the entrance and strtok to break into pieces:

char entrada[100];   // Para obter até 100 caracteres da entrada
int * elementos[10]; // Array com capacidade para 10 elementos
int i = 0;

int tamanhoArray = sizeof elementos / sizeof(int);

if(fgets(entrada, sizeof entrada, stdin) != NULL) {
    for (char *pedaco = strtok(entrada, " "); pedaco != NULL; pedaco = strtok(NULL, " ")) {

        // Se atingir a capacidade do array
        if (i >= tamanhoArray) {
            puts("Não foi possível adicionar mais itens na lista!");
            break;
        }
        elementos[i++] = pedaco;
    }

    for (int n = 0; n < tamanhoArray; ++n) {    
        printf("Indice [%d] = %s\n", n, elementos[n]);
    }
} 

See DEMO

If you prefer to create the array with size based on the number of spaces:

char entrada[100];  // Para obter até 100 caracteres da entrada
int qtdEspacos = 1;
int i = 0;

if(fgets(entrada, sizeof entrada, stdin) != NULL) {
    char *ptr = entrada;

    while((ptr = strchr(ptr, ' ')) != NULL) { // Se encontrou espaço
        qtdEspacos++;
        ptr++;
    }

    // Cria o array com tamanho baseado na quantidade de espaços na string
    int * elementos[qtdEspacos];

    for (char *pedaco = strtok(entrada, " "); pedaco != NULL; pedaco = strtok(NULL, " ")) {
        elementos[i++] = pedaco;
    }

    for (int n = 0; n < qtdEspacos; ++n) {    
        printf("Indice [%d] = %s\n", n, elementos[n]);
    }
}

See DEMO