C structs, strings and segmentation faults [duplicate] - c

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This question already has answers here:
Crash or "segmentation fault" when data is copied/scanned/read to an uninitialized pointer
(5 answers)
Closed 5 years ago.
So this is supposed to be a concordance program where it grabs words from a text file. I'm trying to use a struct to store the string, and also the number of times the word occurs in the text file. I also want to place the struct object into an array of structs, because I will need to sort the words alphabetically once I have them all. However, I'm getting a segmentation fault inside my createStruct function. I know the problem is with my limited knowledge of pointers and passing by reference. I've been messing with createStruct and compareStruct for days now and it just isn't clicking.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
typedef struct word{
char *wordArr;
int wordCount;
}word;
char *makeLowerCase(char word[]);
char *removeFirstChar(char word[]);
char *removeLastChar(char word[]);
void createStruct(struct word wordObj, char word[]);
void structCompare(struct word wordObj, struct word objArr[]);
int main(int argc, char * argv []) {
char buff[] ="##Hello$$$$$"; //hard coded, will grab words from a .txt file
struct word newWord = {.wordArr = NULL, .wordCount = 0};
struct word structArray[500];
makeLowerCase(buff);
removeFirstChar(buff);
removeLastChar(buff);
createStruct(newWord, buff);
structCompare(newWord, structArray);
//trying to print from the array
printf("%s %d", structArray->wordArr, structArray->wordCount);
return 0;
}
char *makeLowerCase(char grabbedWord[]) {
int i;
size_t wordLength = strlen(grabbedWord);
for(i = 0; i < wordLength; i++) {
grabbedWord[i] = tolower(grabbedWord[i]);
}
return grabbedWord;
};
char *removeFirstChar(char inputWord[]) {
int i = 0;
size_t length = strlen(inputWord);
if (!isalnum(inputWord[i])) {
i++;
strncpy(inputWord, &inputWord[i], length);
return removeFirstChar(inputWord);
}
return inputWord;
};
char *removeLastChar(char inputWord[]) {
size_t length = strlen(inputWord);
if (!isalnum(inputWord[length - 1])) {
inputWord[length - 1] = 0;
return removeLastChar(inputWord);
}
return inputWord;
};
void createStruct(struct word wordObj, char string[]) {
strcpy(wordObj.wordArr, string);
wordObj.wordCount = 1;
};
void structCompare(struct word obj, struct word structArr[]) {
int i;
for(i = 0; i < sizeof(structArr); i++) {
if(structArr[i].wordCount == 0) {
strcpy(structArr[i].wordArr, obj.wordArr);
structArr[i].wordCount = obj.wordCount;
}
else if(strcmp(structArr[i].wordArr, obj.wordArr) == 0) {
structArr->wordCount++;
}
else {
strcpy(structArr[i].wordArr, obj.wordArr);
structArr[i].wordCount = obj.wordCount;
}
}
};

Answer 1

You get a segmentation fault because of a NULL pointer.
For copying a string, you use strcpy(char *dest, char *src). But the dest needs to be allocated. In your case, is just NULL;
So this is what you need to do:
// Add a \0 to the end of a string so you know when to stop.
char buff[] ="##Hello$$$$$\0";
// Allocate the char array so you know where to copy it. I allocate it by default to 500, change this based on your needs.
struct word newWord = {.wordArr = (char *)malloc(sizeof(char) * 500), .wordCount = 0};
If you pass the struct to a function directly, you will pass a copy of it so any change done in the function, will not be seen outside of the function. So you need to pass a pointer to the struct instead of the actual struct.