Array of strings reading its input from file.txt C programming

Question

I am having a problem and cant tell what is it.

struct arrayDB {
char *user[MAX_SIZE];
char *pass[MAX_SIZE];
char db[10][2];
};

void readFile(char fileName[100])
{
    char* word ;
    char line[90];
    FILE *passFile;
    int rowC=0;
    int chk=0;

    passFile=fopen(fileName,"rt");
    while(fgets(line,90,passFile)!=NULL)
    {
        word=strtok(line," ");
        rowC=rowC+1;
        while(word!=NULL)
        {
            printf("Count=%i \n",rowC);
            if(chk==0)
            {
                printf("word:%s\n",word);
                DB.user[rowC]=word;
                chk=1;
            }
            else
            {
                printf("word:%s\n",word);
                DB.pass[rowC]=word;

            }
            printf("r=%s , c=%s\n",DB.user[rowC],DB.pass[rowC]);
            word=strtok(NULL," ");

        }

        chk=0;
    }
    int i;

    for(i=1; i<6;i++)
    {
        printf("- %s , %s \n",DB.user[i],DB.pass[i]);
    }

 }

but the output I am getting that all the array elements is the same value which is the last word in the file as you can see in the pic

thanks

Is it really easier to put a screenshot instead of text copy/paste? — Eugene Sh.
– Eugene Sh., Commented Jan 29, 2016 at 20:19
The code you are showing is not the code you ran the example with. For one, in the line DB.pass[rowC]=word; DB is not defined. — ryyker
– ryyker, Commented Jan 29, 2016 at 20:37

Barmar · Accepted Answer · 2016-01-29 20:49:55Z

1

You're reading every line into the same string line. Then when you use strtok(), it's returning pointers into this string, and you're storing these pointers into DB. So all the records in DB are pointing to locations in line, which gets overwritten each time you read another line from the file. When everything is done, line contains the contents of the last line of the file, and all the DB entries point to that.

Another problem is that line is a local variable, and pointers to it become invalid when the function returns.

To solve both problems, you need to make copies of the string and store these in DB. For example:

        DB.user[rowC]= strdup(word);

This also means that when you're done with a DB record, you need to call free(DB.user[i])

answered Jan 29, 2016 at 20:49

Barmar

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Comments

ryyker · Accepted Answer · 2016-01-29 21:23:43Z

1

Some suggestions:

First, learn to use a debugger. There are free ones, get one and turn it on to find all of these errors (that is what I did here)

Next, for the code example you show to compile, the struct definition needs to support your code (currently, DB is not defined)

typedef struct  
{
    char *user[MAX_SIZE];
    char *pass[MAX_SIZE];
    char db[10][2];
}arrayDB;

arrayDB DB;//define DB

Next,

you need to allocate space for your string arrays: something like:

for(i=0;i<MAX_SIZE;i++ )
{
    DB.user[i] = malloc(100);
    DB.pass[i] = malloc(100);
}

Next, don't forget to free them when done using them.

for(i=0;i<MAX_SIZE;i++ )
{
    free(DB.user[i]);
    free(DB.pass[i]);
}

Next, you cannot assign a string using an equal operator:

DB.pass[rowC]=word;

use strcpy (or some other string function) instead:

strcpy(DB.pass[rowC],word);

Next, this line:

printf("r=%s , c=%s\n",DB.user[rowC],DB.pass[rowC]);

Is called after a conditional statement where either DB.user[rowC] or DB.pass[rowC] will be written to, never both. Suggest splitting this printf statement to print one or the other, and place it into the appropriate conditional branch.

edited Jan 29, 2016 at 21:23

answered Jan 29, 2016 at 20:57

ryyker

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3 Comments

SHADOW.NET Over a year ago

thanks for all the tips. The thing is that I am java programmer. but i am trying to do socket programming in C and everything is different in C. Thank you again. I will try to do your recommendations

Barmar Over a year ago

He is incrementing the index. Didn't you see the line rowC = rowC + 1;?

ryyker Over a year ago

Yes. Saw that after I put the last comment in. I will edit that last comment out. Thanks.

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