c-将文件放入字符数组

Question

hi i have the following code below, where i try to get all the lines of a file into an array... for example if in file data.txt i have the following:

first line

second line

then in below code i want to get in data array the following: data[0] = "first line"; data[1] = "second line"

My first question: Currently I am getting "Segmentation fault"... Why?

Exactly i get the following output:

Number of lines is 7475613

Segmentation fault

My second question: Is there any better way to do what i am trying do?

Thanks!!!

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

int main(int argc, char* argv[])
{
 FILE *f = fopen("data.txt", "rb");
 fseek(f, 0, SEEK_END);
 long pos = ftell(f);
 fseek(f, 0, SEEK_SET);

 char *bytes = malloc(pos);
 fread(bytes, pos, 1, f);

 int i =0;
 int counter = 0;
 for(; i<pos; i++)
 {
  if(*(bytes+i)=='\n') counter++;
 }
 printf("\nNumber of lines is %d\n", counter);

 char* data[counter];
 int start=0, end=0;
 counter = 0;
 int length;

 for(i=0; i<pos; i++)
 {
  if(*(bytes+i)=='\n')
  {
   end = i;
   length =end-start;
   data[counter]=(char*)malloc(sizeof(char)*(length));
   strncpy(data[counter],
           bytes+start,
           length);
   counter = counter+1;
   start = end+1;
  }
 }

 free(bytes);
 return 0;
}

First line of the data.txt in this case is not '\\n' it is: "23454555 6346346 3463463".

Thanks!

Answer 1

• You need to malloc 1 more char for data[counter] for the terminating NUL.
• after strncpy , you need to terminate the destination string.

---

Edit after edit of original question

Number of lines is 7475613

Whooooooaaaaaa, that's a bit too much for your computer! If the size of a char * is 4, you want to reserve 29902452 bytes (30M) of automatic memory in the allocation of data .

You can allocate that memory dynamically instead:

/* char *data[counter]; */
char **data = malloc(counter * sizeof *data);

/* don't forget to free the memory when you no longer need it */

---

Edit: second question

My second question: Is there any better way to do what i am trying do?

Not really; you're doing it right. But maybe you can code without the need to have all that data in memory at the same time.
Read and deal with a single line at a time.

You also need to free(data[counter]); in a loop ... and free(data); before the "you're doing it right" above is correct :)

And you need to check if each of the several malloc() calls succeeded LOL

Answer 2

First of all you need to check if the file got opened correctly or not:

FILE *f = fopen("data.txt", "rb");
if(!f)
{
    fprintf(stderr,"Error opening file");
    exit (1);
}

If there is error opening the file and you don't check it, you'll get a seg fault when you try to fseek on an invalid file pointer.

Apart from that I see no errors. Tried running the program, by printing the value of the data array at the end, it ran as expected.

Answer 3

要注意的一件事是，您以二进制格式打开文件-行终止规则可能无法在您的平台上正常运行（UNIX为lf，Windows为cr-lf，某些MacOS版本为cr）。