getline line by line and then store entire lines i

问题:

I'm trying to store every line separately in an array of strings. It doesn't work the way I've written it obviously all I'm getting when I try to print array[0] is the last line of the textfile. But when I print the variable "line" inside of the while loop I can print every single line in the text file but I can only seem to store the last line of the txt file.

Is this possible to do? Or is this a limitation of getline..?

int main()
{
  FILE * fp;
  char *line;
  ssize_t read;
  size_t bufsize = 32;
  int i=0;

  char **array;

  array = malloc(bufsize * sizeof(char));
  line = malloc(bufsize * sizeof(char)); 
  fp = fopen("testing.txt", "r"); 

  while ((getline(&line, &bufsize, fp)) != -1) { 
    printf("%s", line);
    array[i] = line;
    i++;
  } 
  fclose(fp);  
  printf("%s", array[0]);

  return 0;
}

回答1:

As already has been mentioned, you need to allocate space for pointers, not chars:

char **array;
array = malloc(bufsize * sizeof(char*));

Also you need to allocate space for separate lines, and copy lines to it:

while ((getline(&line, &bufsize, fp)) != -1) {
  printf("%s", line);
  array[i] = malloc(strlen(line) + 1);
  strcpy(array[i], line);
  i++;
} 

A mistake in your code is that all array[i] points to the same string in variable line, which is refilled by getline() every loop cycle.

It may be useful to read manual about getline. It permits allocation of strings by itself, but don't forget to use free().

array[0] = NULL;
while ((getline(&array[i], &bufsize, fp)) != -1) {
  printf("%s", array[i]);
  array[i + 1] = NULL;
  i++;
} 

回答2:

char **array;



array = malloc(bufsize * sizeof(char));

array[i] = line;

I think your problem is with array, you are indeed dynamically allocating memory for array but not array[i].

while ((getline(&line, &bufsize, fp)) != -1) { 
array[i]=malloc(sizeof(char) * (bufsize+1));
printf("%s", line);
array[i] = line;
i++;

}

This should fix it

Edit after testing the program:

array = malloc(bufsize * sizeof(char));

should be

array = malloc(bufsize * sizeof(char*));

回答3:

This does not make an array of strings:

char **array;
array = malloc(bufsize * sizeof(char));

There are plenty of resources that describe how to do this. eg. How to create a dynamic array of strings. Essentially, you need to allocate space for the array, then allocate space for each the strings, a standard way might be:

char **arrayOfStrings;
unsigned int numberOfElements = 20, sizeOfEachString = 100;
arrayOfStrings = malloc(numberOfElements * sizeof(char*));
for (int i = 0; i < numberOfElements ; i++)
    arrayOfStrings[i] = malloc(sizeOfEachString  * sizeof(char));

As a further note, for your whileloop:

while (getline(&line, &bufsize, fp)) {

Is sufficient. Getline will return 0 once you have finished your file. Read this.