CODEWITHSUNDEEP
cfileunix
Ilan Aizelman WS
Ilan Aizelman WS

Reputation: 1632

Reading a line from a file and storing it in variables

I've got a file with 2-3 lines, and every line I want to store in a char* variable, then translate it and store it to other appropriate variables.

not in unix, just in c, there's a fscanf(%d,%s,%s, 1,2,3); and thats it, but in unix it is somewhat weird.

For example: a abc 12 12

Storing it in char msg[20], and then msg[20] will be stored in 4 variables, one char, one char* and two integers. How can It be done?

Here what I got so far:

int ret_in, in1,file;
char buffer1[BUF_SIZE];
int i =0;

    char fn[5] = "file";

      char msg[20];
     file = open(fn,O_WRONLY|O_CREAT,0644);
     //msg = "test";

    while(((ret_in = read (file, &buffer1, BUF_SIZE)) > 0))
      {
       for(i; i<ret_in; i++)
        {
         if(buffer1[i]!='\n')
          msg[i] = buffer1[i];
        }
    }
    printf("%s", msg); //TEST: check msg
    close(file);

It stores it fine in the msg variable, but if it composed of 4 'items' i want to store in different variables, how can I do it efficiently?

Upvotes: 1

Views: 3103

Answers (1)

ad absurdum
ad absurdum

Reputation: 21316

You can use fopen() to open a file and get a pointer to a file stream. This pointer can be passed to fgets() to retrieve lines from the file and store them in a buffer. This buffer can then be parsed by using sscanf().

Here is an example of how this might work. Note that here I am using arrays to store the components of the fields from each line; you may have different requirements.

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

#define MAX_LINES  100

int main(void)
{
    FILE *fp = fopen("my_file.txt", "r");
    if (fp == NULL) {
        perror("Unable to open file");
        exit(EXIT_FAILURE);
    }

    char buffer[1000];
    char id[MAX_LINES];
    char msg[MAX_LINES][10];
    int val_a[MAX_LINES];
    int val_b[MAX_LINES];
    size_t lines = 0;

    while (fgets(buffer, sizeof buffer, fp) != NULL) {
        if (sscanf(buffer, "%c%9s%d%d",
                   &id[lines], msg[lines], &val_a[lines], &val_b[lines]) == 4) {
            ++lines;
        }
    }

    for (size_t i = 0; i < lines; i++) {
        printf("Line %zu: %c -- %s -- %d -- %d\n",
               i+1, id[i], msg[i], val_a[i], val_b[i]);
    }

    fclose(fp);

    return 0;
}

Using this text file as input:

A abc 12 34
B def 24 68
C ghi 35 79

gives the following output:

Line 1: A -- abc -- 12 -- 34
Line 2: B -- def -- 24 -- 68
Line 3: C -- ghi -- 35 -- 79

Upvotes: 1

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