分段错误：循环打印时为11

Question

First of all say that I have been looking for information on the network, making tests with gdb debugging and...nothing...I still do not understand the error, I get the idea that it might come from the "getline" instruction, but I'm not sure...

The main idea of the code is to read line by line and convert chars strings into floats and save the floats in a array called nfloat and then call the function: *create_table* to create an array of pointers of type vector.

The input is a .txt containing this: n = the number of strings, in this case n = 3

3
[9.3,1.2,87.9]
[1.0,1.0]
[0.0,0.0,1.0]

The first number, 3 is the number of vectors as we can see in the image, but that number isn't static, the input can be 5 or 7 , etc instead of 3 .

So far, I've started doing the following, but the code has some memory errors I think:

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


typedef struct {
    float* data;
    int size;
} vector;




vector *create_vector(int n, float* comps){
    vector newvect;
    newvect.data = (float *) malloc(n*sizeof(float));
    int i;
    for(i = 0; i < n; i++) {
        newvect.data[i] = comps[i];
        printf("Newvec.data[%d] = %.1f\n", i, newvect.data[i]);
    }
    newvect.size = n;
    vector *pointvector;
    pointvector = &newvect;
    return(pointvector);
}


int NumsVector(char *linea, ssize_t size){
    int numsvector = 1; 
    int n;
    for(n = 2; n<= size; n++){ 
        if (linea[n] != '[' && linea[n] != ']'){
            if(linea[n] == 44){
                numsvector = numsvector + 1;
            }
        }
    }
    return numsvector;
}

int main(){
    int n, i;
    scanf("%d\n", &n);
    vector *v[n];
    for(i = 0; i<n; ++i) { 
        char *line = NULL; 
        size_t len = 0;
        ssize_t read; 
        read = getline(&line,&len,stdin);
        int numsvector = NumsVector(line, read);
        float nfloat[numsvector];
        int j = 0;
        /* Replaces the end ] with a , */
        line[strlen(line) - 1] = ',';

        /* creates a new pointer, pointing after the first [ in the original string */
        char *p = line + 1;
        do
        {
            /* grabs up to the next comma as a float */
            sscanf(p, "%f,", &nfloat[j]);
            /* moves pointer forward to next comma */
            while (*(p++) != ',');
        }
        while (++j < numsvector); /* stops when you've got the expected number */
        v[i] = create_vector(numsvector, nfloat);
        printf("%f\n", v[i]->data[1]); //prints ok :)!
        free(line);
    }
    printf("%f\n", v[i]->data[1]); //segmentation fault:11 :(!! }

Well, the problems come with the printf instructions I think, when I print inside the loop, everything works fine but when I try to do the same out of the for loop, it prints the segmentation fault error...might be some memory leak?

is important for me to know if *v[n] is well implemented and stores well the information in order to keep creating functions based on the *v[n] information.

Please could someone help me understand where is the problem when I print out the loop?

Answer 1

vector *pointvector;
pointvector = &newvect;
return(pointvector);

You're returning pointer to local variable. This is incorrect and needs to be changed either by allocating dynamic memory for newvect or by using static variable within function and then copying data (data wouldn't persist between two calls).

Edit: as requested, example with dynamic allocation:

vector *create_vector(int n, float* comps){
    vector *newvect = malloc(sizeof(*newvect));
    newvect->data = malloc(n*sizeof(float));
    memcpy(newvect->data, comps, sizeof(float) * n);
    newvect->size = n;
    return newvector;
}

Of course at some point you'll need to free both data and vector itself.

Answer 2

In this line

printf("%f\n", v[i]->data[1]); //segmentation fault:11 :(!! }

i equals n . And as v is declared v[n] the above line provokes undefined behaviour by accessing v out of bounds.

---

To get around the issue of returning an address to a local variable do like this:

vector * create_vector(size_t n, float * comps)
{
  vector * newvect = malloc(sizeof(*newvect);
  if (NULL != newvect)
  {
    return NULL;
  }

  newvect->data =  malloc(n * sizeof(*newvect->data));
  if (NULL != newvect->data)
  {
    free(newvect);
    return NULL;
  }

  for(size_t i = 0; i < n; i++) 
  {
    newvect->data[i] = comps[i];
    printf("newvect->data[%zu] = %.1f\n", i, newvect->data[i]);
  }

  newvect->size = n;

  return newvect;
}