Question

I don’t work with C often so please excuse any mistakes I might be making in terms of coding style 😛 I’m currently getting an error that I’m a bit stumped on: when I include the line tokenCopy = malloc(sizeof(fileSize));, I get random a random exclamation about 1/4th of the way through the output of a file to std but if the line is removed/commented, the data displays as expected:

MAY      +1.32      D1      1002
JUNE     -1.57      D3      201
JULY      -2.37      D4      478
AUGUST      +5.03      D2      930
SEPTEMBER      -3.00      D1      370
OCTOBER      +7.69      D1      112

and the actual output I get when the line is in place:

MAY      +1.32      D1      1002
JUNE      -1.57      D3      2!

and the relevant code:

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


    /**
     * Machine struct - three column
     **/

    /**
     * Parses the input file, size is the size of name
     **/

    char parseInputFile(char *name, int size) {
            FILE *fp;

          if ((fp = fopen(name,"r")) == NULL) {
                printf("Cannot open file %s\n", name);
                return 1;
            }
            else {
                int fileSize;
                fileSize = 0;
                char *fileContent;
                char *processedFileContent;

                //get file size
                fseek(fp, 0, SEEK_END);
                fileSize = ftell(fp);
                fseek(fp, 0, SEEK_SET);

                //allocate
                fileContent = malloc(sizeof(fileSize));
                processedFileContent = malloc(sizeof(fileSize));

                //read
                char c;
                int g;
                g=0;

                while((c = getc(fp)) != EOF) {
                    fileContent[g] = c;
                    g++;
                }

                //process
                char delim[6] = "      ";
                char *tokenCopy;
                tokenCopy = malloc(sizeof(fileSize));

                strcpy(tokenCopy, fileContent);
                char *tokens = strtok(tokenCopy, delim);

                while (tokens) {
                    tokens = strtok(NULL, delim);
                }

                puts(fileContent);
                //printf("File Size: %i \n",fileSize);
                //puts(tokenCopy);
                return *processedFileContent;
            }
    }

    int main(int argc, char *argv[])
    {
            //char *input;
            if (argc == 1)
                puts("You must enter a filename");
            else {
                int size = sizeof(argv[1]);
                parseInputFile(argv[1],size);
            }
            return 0;
    }

---

Could anyone offer any insight into what I’m doing wrong (or if my code is causing problems in itself)?

Answer 1

You put the size of the file in fileSize but then allocate only the space to store an int that is what sizeof(FileSize) will give you.

These two lines

            fileContent = malloc(sizeof(fileSize));
            processedFileContent = malloc(sizeof(fileSize));

should be (assuming you will treat the text you’ll read as a string):

            fileContent = malloc(fileSize+1);
            processedFileContent = malloc(fileSize+1)

and, after having read the file content, you should put a ‘\0’ at the end.

That said, I really don’t get what you are trying to achieve by using strtok(). If you only need to separate the three components of each line, you can do it much easily while you read the file since you read it one character at the time.

If you elaborate a little bit more on what you’re trying to achieve, we might have other advice.

UPDATE AFTER COMMENT BELOW

You should step back a second and reconsider your problem as I suspect you don’t need to store any string at all. The first value is a month name, which can be stored as an integer, the second is a double (or float), the third seems ‘Dx‘ with x varying from 1 to 4, again this could be an integer. It seems the name of a sensor, so I suspect it could be coded in an integer anyway as there will surely be a finite number of them. And the fourth is clearly another integer.

With a wild guess on what those fields mean, your struct would look like something like this:

struct val {
   int month;
   double value;
   int sensor;
   int var;
}

Now, you can get the values as you go one char at the time, or read an entire line and get the values from there.

Going one char at the time will not require any additional space but will result in a longer program (full of ‘if’ and ‘while’). Reading the line will be slightly easier but will require you to handle the maximum size of a line.

A proper structuring of functions will help you a lot:

 do {
   if ((c = get_month(fp, &month)) != EOF) 
     if ((c = get_value(fp, &value)) != EOF)
       if ((c = get_sensor(fp, &sensor)) != EOF)
         if ((c = get_var(fp, &var)) != EOF)
           measures = add_data(measures, month, value, sensor, var);
 } while (c != EOF);
 return measures

Where measures can be a linked list or a resizable array of your structs and assuming you’ll go one char at the time.

There are quite many other details you should set before you’re done, I hope this will help you find the right direction.