C: Strings, segmentation error

Question

The following piece of code is scanning for command line arguments for valid sentences that contains the words 'Int' or 'Float'.

I have debugged it for hours trying to locate where the error is occurring to no avail.

Any help would be appreciated.

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

bool process_input(int, char *[]);
bool first_word_correct(char *);
void print_string(char *);

int main(int argc, char *argv[]) {
    if (!process_input(argc, argv))
        printf("Incorrect input.\n");
    else
        printf("CORRECT input.\n");

    return EXIT_SUCCESS;
}

bool process_input(int argc, char *argv[]) {
    char *word;
    int i, j;
    bool is_new_sentence = true;

    i = 0;
    j = 0;

    while (++i < argc) {
        // check the first word - must be "A" or "An"

        if (is_new_sentence) {            
            if (!first_word_correct(argv[i])) {
                return false;
            }

            is_new_sentence = false;
        }

        // we're checking subsequent words of the same sentence

        else if (!is_new_sentence) {
            // is this the last word?

            strcpy(word, argv[i]);

            if (word[strlen(word) - 1] == '.') {
                is_new_sentence = true;
            }

            switch(is_variable_name(word)) {
                case 1:
                    printf("int found!\n");
                    break;
                case 2:
                    printf("float found!\n");
                    break;
            }
        }
    }

    return true;
}

bool first_word_correct(char *word) {    
    if (strcmp(word, "A") == 0 || strcmp(word, "An") == 0) {
        return true;
    }
    else {
        return false;
    }
}

/*
 *int 1
 *float 2
 */

int is_variable_name(char *word) {
    if ((strcmp(word, "int") == 0) ||  (strcmp(word, "int.") == 0))
        return 1;

    if ((strcmp(word, "float") == 0) ||  (strcmp(word, "float.") == 0))
        return 2;

    return -1;
}

you need to allocate memory for word before you strcpy(word, argv[i])... or you could avoid the copy if you are not going to modify the word. — SleuthEye
– SleuthEye, Commented Oct 29, 2014 at 4:07
If I am not modifying the word, what should I use to copy the string? — Damien Lowe
– Damien Lowe, Commented Oct 29, 2014 at 4:17
If you're using strcpy, it creates a new string, and so you cannot send a dangling pointer — nj-ath
– nj-ath, Commented Oct 29, 2014 at 4:20
@DamienLowe as you are not modifying the input, you can just use: char* word = argv[i]; — Baldrickk
– Baldrickk, Commented Oct 29, 2014 at 9:37

Anbu.Sankar · Accepted Answer · 2014-10-29 04:10:22Z

3

You are not allocated memory for word before using it. Try like

       else if (!is_new_sentence) {
        // is this the last word?
        word=malloc(100);// size is based on your argv[i]
        strcpy(word, argv[i]);

        if (word[strlen(word) - 1] == '.') {
            is_new_sentence = true;
        }

answered Oct 29, 2014 at 4:10

Anbu.Sankar

1,3468 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

Anbu.Sankar Over a year ago

@P0W ofcourse i wont forget. Just for giving an idea i have written.

P0W Over a year ago

That was for OP, never mind, it always a good practice to write that in answer, if OP is unaware of it, s(he) may end up leaking resources

Damien Lowe Over a year ago

I added word=malloc(sizeof(argv[i]), and now I am getting an error indicating an 'invalid pointer' and then aborting.

P0W Over a year ago

@DamienLowe sizeof(argv[i]) will give you size of pointer, not the length of argv[i]

Anbu.Sankar Over a year ago

@POW word=malloc(strlen(argv[i])+1);// 1 is for NULL

|

Collectives™ on Stack Overflow

C: Strings, segmentation error

1 Answer 1

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related