getc Seg Fault

**Tyris** · 05-25-2005

Hi all,
once again, its 3am, and I'm desperately trying to finish a C program in time.
Basically, we have to write a program to demonstrate some hash tables etc... nothing too complicated (at least I expect this would be so had I gone to my lectures

).
My problem is, that I seem to be getting a seg fault on windows -and- unix, upon getting to the getc function (or macro or whatever it is).

The file seems to open correctly... (the actual code has error checking etc...)

Code:

data = fopen(data_file,"r"))

I can also do fgets and read in entire lines... but when i try getc (or fgetc) i get a segmentation fault.

Code:

    char c; // current character
    char currword[TMP_WORD_LEN]; // current word
    char *new_word; // Pointer to words that will be added to the array
    int i=0; // word index counter
    int wc=1; // word length counter
    while(c = getc(data))

(note: 'data' is sent thru in the function header as (FILE *), however the same error occurs if i try to do the getc directly after opening the file)
Prior to this, some other functions are called... one to initialise an empty hash table

Code:

void create_hash_table(int size)
{
    printf("size: %d\r\n",size);
    hash_table = malloc(size*sizeof(struct hash));
    int i;
    for(i=0;i<=size;i++)
    {
        hash_table[i].contents = "NULL";
        hash_table[i].occurances = 0;
    }
    return;
}

... and some basic arguement parsing...

Thats... about it...
O... except, that If i run in debugging mode (Dev-C++ 4.9.9.2), the program works perfectly (performs everything as expected)... unfortunately if it doesnt compile outside debugging... i get nothing ^^;;

Any help would be greatly appreciated... in the mean time.. I might catch some shut eye (starting at the words "(c = getc(data))" for hours doesnt really help...)

Thanks in advance

**Salem** · 05-25-2005

Code:

int c;
while( (c = getc(data)) != EOF )

> char *new_word;
Where is this pointing?
If you don't initialise it, then seg faults can't be far away.

Seriously, there's not enough information in your post to determine why it crashes.

**Tyris** · 05-25-2005

new_word is malloc'd later in the program...

*edit*
also, adding the !=EOF bit, doesnt help, and its only missing coz i check elsewhere (cant remember why XD )

The reason I'm quite sure its getc, is that if i put a print statement immediately before, and immediately after
eg:

Code:

printf("before\r\n");
c = getc(data);
printf("after\r\n");

The first print statement will appear, then it will seg fault...
That said, I'll attach a bit more of my code =S

Code:

int main(int argc, char *argv[])
{
    create_hash_table(hash_total); // Set empty hash table
    hash_type(0);
    int verbose=0;
    FILE *data;
    char *data_file="NULL";
    FILE *search;
    char *search_file="NULL";
    char tmp_arg;
.....
    if(strcmp(data_file,"NULL")==0)
    {
        printf("No input file specified...\r\n");
        return 0;
    }
    if((data = fopen(data_file,"r")) == NULL)
    {
        printf("Textfile failed to load...\r\n");
        return;
    }
    prepro_words(data);
......
void prepro_words(FILE *data)
{
    char c; // current character
    char currword[TMP_WORD_LEN]; // current word
    char *new_word; // Pointer to words that will be added to the array
    int i=0; // word index counter
    int wc=1; // word length counter
    while(c = getc(data))
    {
            if(i>=wc*TMP_WORD_LEN)
            {
                int owc = wc++; // old word length counter
                char tmp_word[owc*TMP_WORD_LEN];
                strncpy(tmp_word,currword,owc*TMP_WORD_LEN-1);
                free(currword);
                char currword[wc*TMP_WORD_LEN];
                strncpy (currword,tmp_word,owc*TMP_WORD_LEN-1);
                free(tmp_word);
            }
            if(isalpha(c))
                currword[i++] = (char) tolower((int) c);

.... etc

**itsme86** · 05-25-2005

adding the !=EOF bit, doesnt help

That's because getc() returns an int, but you have c defined as a char. It will never match EOF as long as c is defined as a char.

Also, why are you free()'ing non-malloc()'d memory?

Code:

    char currword[TMP_WORD_LEN]; // current word
                char tmp_word[owc*TMP_WORD_LEN];
                free(currword);
                char currword[wc*TMP_WORD_LEN];
                free(tmp_word);

You can't do this. You can only free() memory that's been allocated via malloc() and friends.

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