Read lines from file not return all

Question

I'm trying to keep the words from a file into an array but I only read the first 8.

My code below.

#define BUF 128 /* can change the buffer size as well */


char ** readFileContentArray(char* filename){

   int lines = 128;
   char **     strLines = (char **)malloc(sizeof(char*)*lines);
   FILE *plist = NULL;
   int i = 0;

   char line[4];

   plist = fopen(filename, "r");
   while(fgets(line, BUF, plist)) {

       if(i >= lines){
           strLines = (char **)realloc(strLines, (lines*2) * sizeof(char *));
           lines = lines*2;
       }

       strLines[i] = strdup(line);
       i++;
   }


   return strLines;
}

The file that I'm reading is formed like below:

aaaa

bbbb

cccc

dddd

eeee

ffff

gggg

hhhh

iiii

jjjj

1) "_`fgets(line, BUF, plist)`_" -- You are allowing `fgets` to store a maximum of 128 characters into `line` which can hold just 4 characters 2) You don't check the result of `fopen` 3) Don't cast the result of `calloc`/`malloc`/`realloc` in C — Spikatrix, Jun 08 '15 at 10:38
Use the size of array directly in the call: `fgets(line, sizeof line, plist)` — pmg, Jun 08 '15 at 10:53
You should consider using [getline(3)](http://man7.org/linux/man-pages/man3/getline.3.html) if it is available on your (e.g. POSIX) system. — Basile Starynkevitch, Jun 08 '15 at 10:54

score 3 · Accepted Answer · answered Jun 08 '15 at 14:46

You could pass pointers to two integers so the caller can tell how many items are allocated in the array.
Call as char **strArray = readFileContentArray ( "file.txt", &total, &used);
The results may be printed with

for ( i = 0; i < used; i++) {
    printf ( "%s", strArray[i]);
}

and similarly free'd.

for ( i = 0; i < used; i++) {
    free ( strArray[i]);
}
free ( strArry);

these would be used in the calling function.

char ** readFileContentArray(char* filename, int *lines, int *used){

    *lines = 128;
    *used = 0;
    char **strLines = malloc(sizeof(char*)*(*lines));
    char **strTemp = NULL;
    FILE *plist = NULL;

    char line[6];

    plist = fopen(filename, "r");
    if ( plist == NULL) {
        return NULL;
    }
    while(fgets(line, sizeof ( line), plist)) {
        if ( line[0] == '\n') {
            continue;//blank line
        }
        if(*used >= *lines){
            strTemp = realloc(strLines, ((*lines)*2) * sizeof(char *));
            if ( strTemp == NULL) {
                printf ( "realloc failed\n");
                return strLines;
            }
            strLines = strTemp;
            *lines = (*lines)*2;
        }
        strLines[*used] = strdup(line);
        *used += 1;
    }
    return strLines;
}

score 2 · Answer 2 · edited May 23 '17 at 12:22

2

Your code has several problems.

Don't cast the result of malloc/calloc/realloc in C
You don't check if fopen was successful. This can be done by checking its return value. fopen returns NULL on failure.
You allow fgets to write 128 characters into line, which can at most hold 4 characters.

Fixed code:

#define BUF 128 /* Change to max size of a line */


char ** readFileContentArray(char* filename){

   int lines = 128;
   char **     strLines = malloc(sizeof(char*) * lines);

   if(strLines == NULL) //If malloc failed
       return NULL; 
   FILE *plist = NULL;
   int i = 0;

   char line[BUF]; //Allocate BUF size

   if((plist = fopen(filename, "r")) == NULL) //If fopen failed
       return NULL; 
   while(fgets(line, BUF, plist)) { 

       if(i >= lines){
           char* temp;
           if((temp = realloc(strLines, (lines*2) * sizeof(char *))) == NULL) //If realloc failed
           {
               free(strLines);
               return NULL;
           ]
           lines = lines*2;
       }

       strLines[i] = strdup(line);
       i++;
   }

   fclose(plist); //Close file after its use

   return realloc(strLines, i * sizeof(char*)); //Return correct size
}

edited May 23 '17 at 12:22

Community

1
1

answered Jun 08 '15 at 10:45

Spikatrix

19,653
7
38
77

Sorry, maybe not I havent explained well. My array only stored 8 lines, but the file contains many more (about 200.000). I try your code but only can stored the first eight. – jlopez Jun 08 '15 at 11:01
Thank you very much for your help, but unfortunately still not working – jlopez Jun 08 '15 at 14:46
1

@jlopez , "_not working_" is a bad explanation. How is it not working? – Spikatrix Jun 08 '15 at 14:47
I mean, that only still saving 8 words – jlopez Jun 08 '15 at 14:48
@jlopez , I cannot reproduce that. Consider posting an [MCVE](http://stackoverflow.com/help/mcve) – Spikatrix Jun 08 '15 at 14:49

Read lines from file not return all

2 Answers2