Bus Error with strncpy in C

Question

I am working on the same project as in this question, however with a slightly different typedef:

typedef struct {
    char* word;
    int index;
} data_t;

typedef struct node node_t;

typedef node {
    void *data;
    node_t *left;
    node_t *right;
}

I am trying to split a string into individual words, sticking it into the data_t struct and then inserting it into a binary search tree. The idea is that, while looping across an input string, when it is found that the character is one which marks the end of a word, the number of characters between the start and end of the word is copied into a string, which I have attempted to do using:

strncpy(newstring, (in+wordstart), (i-wordstart));

where:

char* newstring, in;
int i, wordstart;

However, gcc gives a bus error when that particular line is called. How this bus error can be fixed and the current solution kept, or would it be wiser to look for a different solution?

The only idea I have been able to think of so far is to, one character at a time, put the characters into the string until the end of the word has been reached.

`char* newstring, in` are just pointers to some random memory. You do need to make them point to some valid memory, memory belonging to the process. — alk, Oct 23 '12 at 07:46
yeah memory wasn't being allocated at all. sticking in `newstring = malloc(strlen(in)-wordstart);` seems to make it work. — disgruntledperson, Oct 23 '12 at 07:50
Consider allocating `+1` character to store the 0-terminator. @disgruntledperson — alk, Oct 23 '12 at 07:59

score 4 · Answer 1 · answered Oct 23 '12 at 07:50

4

This doesn't declare two pointers, this is just one pointer and a char

char* newstring, in;

It should be declared like this:

char *newstring, *in;

Also, as someone else noted, it doesn't seem that you're allocating any memory for those pointers.

answered Oct 23 '12 at 07:50

iabdalkader

17,009
4
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1

Good catch! And another nice example why to always declare a variable on it's own line! ;-) – alk Oct 23 '12 at 08:01
haha very good point there and thanks for pointing it out! Honestly I put that there to indicate how the strncpy line was type defined. in is passed in to the function via `char *in`, though `newstring` was declared as above. Apologies for that though I will keep your point in mind :) – disgruntledperson Oct 23 '12 at 08:05

score 1 · Answer 2 · answered Oct 23 '12 at 08:07

This:

typedef node {
    void *data;
    node_t *left;
    node_t *right;
}

doesn't make any sense at all. There's no struct keyword before the node, and no name for the type alias you're trying to introduce after the }, and no terminating semi colon. This shouldn't compile.

Bus Error with strncpy in C

2 Answers2