strstr() function get the position

Question

There are two text, text a is content and text b is list out the words line by line. The program is to get the position of words from text b in the content.

This is my program:

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

#define WORDMAXLENGTH 30
#define MAXLENGTH 200

int main(){
    typedef struct{
        char stack[MAXLENGTH][WORDMAXLENGTH];
        int top;
    }stack;

    stack query;
    query.top = 0;
    int i = 0, j = 0,q = 0;
    char myArr[MAXLENGTH];
    char *PosStr = NULL; 
    FILE *inFile = fopen("query.txt","r");
    FILE *inFile2 = fopen("hello.txt","r");

    while(fgets(query.stack[query.top],WORDMAXLENGTH,inFile) != NULL){
        query.top++;
    }

    fgets(myArr,MAXLENGTH,inFile2);

    for(i = 0; i < query.top; i++){
        PosStr = strstr(myArr,query.stack[i]);//get the position of s2 (Q1)
        printf("%d\n", PosStr -  myArr + 1);
    }

    fclose(inFile);
    fclose(inFile2);
    return 0;
}

Q1. Is this equation right? If it is wrong, how can I get the position? If it is right, why I can't get the position correctly? In addition, some of the result of PosStr is 0.

Answer 1

I presumed that the program is intended to check each of the word list in the first file, for occurrence in the single text line of the second file, and with a few tweaks, it works.

I added some error checking and removed the trailing newline from the file inputs. I checked the result of strstr() before printing values based on NULL. I also added another #define to distinguish the size of the stack from the length of the test string, and, I check the stack does not overflow.

UPDATE revises the code to check whole words - case insensitive.

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

#define WORDMAXLENGTH 30
#define MAXENTRY 200
#define MAXLENGTH 200

typedef struct{
    char stack[MAXENTRY][WORDMAXLENGTH];
    int top;
} stack;

int main(){
    FILE *inFile;
    FILE *inFile2;
    int i, w;
    char myArr[MAXLENGTH];
    char *sptr; 
    stack query;
    query.top = 0;
    inFile = fopen("query.txt","r");
    inFile2 = fopen("hello.txt","r");
    if (inFile == NULL || inFile2 == NULL) {
        printf("Cannot open both files\n");
        return 1;
    }
    while(fgets(query.stack[query.top], WORDMAXLENGTH, inFile) != NULL){
        i = strcspn(query.stack[query.top], "\r\n");
        query.stack[query.top][i] = 0;      // remove trailing newline etc
        if (++query.top >= MAXENTRY)        // check stack full
            break;
    }

    fgets(myArr,MAXLENGTH,inFile2);
    //myArr [ strcspn(myArr, "\r\n") ] = 0; // remove trailing newline etc
    w = 1;                                  // word count
    sptr = strtok(myArr, " \t\r\n");        // removes trailing stuff anyway
    while (sptr) {                          // each word in test string
        for(i=0; i<query.top; i++) {        // each word in library list
            if (stricmp(sptr, query.stack[i]) == 0)  // without case
                printf("%-4d %s\n", w, query.stack[i]);
        }
        w++;
        sptr = strtok(NULL, " \t\r\n");
    }

    fclose(inFile);
    fclose(inFile2);
    return 0;
}

File query.txt:

cat
dog
fox
rabbit

File hello.txt:

A quick brown fox jumps over the lazy dog

Program output:

4    fox
9    dog