Read txt file line by line into char array C

Question

I know this question has been asked a few times, but never in a way that helps me figure out my problem. Essentially, I am reading four text files, all single words separated by a new line, and wanting to store these in a char array. I first count the number of lines in the file and then create a new char array, but for the life of me, I cannot figure out how to get it to read correctly. The last two lines are just to test if it has read the entire file correctly and they always come back a NULL and the question mark symbol.

I want each line to be at the next index in the char array.

Any help would be awesome! Thank you ahead of time.

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

void countAnagrams(char* fileName);

void main ()
{
    char *fileNames[] = {"AnagramA.txt","AnagramB.txt","AnagramC.txt","AnagramD.txt"};

    countAnagrams(fileNames[0]);
    countAnagrams(fileNames[1]);
    countAnagrams(fileNames[2]);
    countAnagrams(fileNames[3]);
}

void countAnagrams(char* fileName)
{
    int anagramCount = 0;
    int ch, lines = 0;  

    //Count number of lines in file
    FILE *myfile = fopen(fileName, "r");
    do
    {
        ch = fgetc(myfile);
        if(ch == '\n')
            lines++;
    }while(ch != EOF);

    char contents[lines];
    int i = 0;
    for(i=1;i<lines;i++)
    {
        fscanf(myfile,"%s",contents[i]);
    }
    fclose(myfile);

    printf("%.12s\n",fileName);
    printf("number of lines: %d\n", lines);

    printf("first thing: %s\n", contents[0]);
    printf("last thing: %s\n", contents[lines-1]);
}

"four text files, all single words separated by a new line," so that means lines++; occurs 3 times? — chux
– chux, Commented Sep 12, 2016 at 22:27
Enable warnings, your compiler wants a serious talk with you. And char contents[lines]; is an array of char. Too many errors in your code. — too honest for this site
– too honest for this site, Commented Sep 12, 2016 at 22:27
After counting the lines your file pointer is at the end of the file. You need to close and reopen the file or simply rewind. — kaylum
– kaylum, Commented Sep 12, 2016 at 22:27
After rewind(), you may want for(i=0;i<lines;i++) or for(i=0;i<=lines;i++) — chux
– chux, Commented Sep 12, 2016 at 22:29

rphv · Accepted Answer · 2016-09-13 02:20:48Z

Here's a slight modification of your code that might help you.

The main points:

You can use getline() instead of fscanf(). fscanf() can be used to read line-by-line, but it needs an explicit check for the end of line condition. getline() does this automatically.

As kaylum pointed out, it's necessary to rewind() the file pointer back to the beginning of the file after counting the number of lines.

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

void countAnagrams(char* fileName);                                                                    

void main ()                                                                                           
{                                                                                                      
    char *fileNames[] = {"AnagramA.txt","AnagramB.txt","AnagramC.txt","AnagramD.txt"};                 

    countAnagrams(fileNames[0]);                                                                       
    countAnagrams(fileNames[1]);                                                                       
    countAnagrams(fileNames[2]);                                                                       
    countAnagrams(fileNames[3]);                                                                       
}                                                                                                      

void countAnagrams(char* fileName)                                                                     
{                                                                                                      
    int anagramCount = 0;                                                                              
    int ch, lines = 0;                                                                                 

    //Count number of lines in file                                                                    
    FILE *myfile = fopen(fileName, "r");                                                               
    do                                                                                                 
    {                                                                                                  
        ch = fgetc(myfile);                                                                            
        if (ch == '\n')                                                                                
            lines++;                                                                                   
    } while (ch != EOF);                                                                               

    rewind(myfile);                                                                                    

    char *contents[lines];                                                                             
    int i = 0;                                                                                         
    size_t len = 0;                                                                                    
    for(i = 0; i < lines; i++)                                                                         
    {
        contents[i] = NULL;
        len = 0;                                                                                
        getline(&contents[i], &len, myfile);                                                           
    }                                                                                                  
    fclose(myfile);                                                                                    

    printf("%.12s\n",fileName);                                                                        
    printf("number of lines: %d\n", lines);                                                            

    printf("first thing: %s\n", contents[0]);                                                          
    printf("last thing: %s\n", contents[lines-1]);                                                     
}

You need to set contents[i] to 0 (NULL) before using it in the call to getline(), and I would set len = 0; on each iteration too. That way, getline() knows it needs to allocate each time. With indeterminate values in content entries and an increasing length in len, you have a recipe for major unpleasantness.
If the text file does not end with ` '\n', contents[lines] will be 1 too small.

np_6 · Accepted Answer · 2016-09-12 22:53:23Z

0

I think that the problem is char contents[lines] and then fscanf(myfile,"%s",contents[i]) and the printf-s after. contents[i] is char type, and you want to read an array of chars into one char. contents needs to be declared as char* contents[lines] to be able to read a char array into contents[i].

answered Sep 12, 2016 at 22:53

np_6

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1 Comment

kaylum Over a year ago

That's one of the problem and by no means the first problem that the code encounters. And the suggested solution of declaring a char * array is incomplete as memory would need to be allocated for each entry.

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