CODEWITHSUNDEEP
carraysmemorystrcpy
Anton
Anton

Reputation: 1515

Function strcpy() changes value of integer array?

I'll start off with the code I have currently where input is a user provided variable:

int current[2] = {-1, -1}, next[2] = {-1, -1};
char *strtok_result = strtok(input, " ");
int i = 0;
while(strtok_result != NULL){
    i++;
    int count = 0;
    char strtok_buffer[2];
    printf("iteration %d-%d: next[0] = %d\n", i, ++count, next[0]);
    strcpy(strtok_buffer, strtok_result);
    printf("iteration %d-%d: next[0] = %d\n", i, ++count, next[0]);

    current[0] = next[0];
    current[1] = next[1];
    next[0] = strtok_buffer[1] - 48;            // ascii conversion, digit to column
    next[1] = toupper(strtok_buffer[0]) - 64;   // --- || ---, letter to row
    printf("iteration %d-%d: next[0] = %d\n\n", i, ++count, next[0]);
    strtok_result = strtok(NULL, " ");
}
return 0;

If I enter "A1 B2 C3" I expect the following output:

iteration 1-1: next[0] = -1
iteration 1-2: next[0] = -1
iteration 1-3: next[0] = 1

iteration 2-1: next[0] = 1
iteration 2-2: next[0] = 1
iteration 2-3: next[0] = 2

iteration 3-1: next[0] = 2
iteration 3-2: next[0] = 2
iteration 3-3: next[0] = 3

The output I receive however looks like the following:

iteration 1-1: next[0] = -1
iteration 1-2: next[0] = -256
iteration 1-3: next[0] = 1

iteration 2-1: next[0] = 1
iteration 2-2: next[0] = 0
iteration 2-3: next[0] = 2

iteration 3-1: next[0] = 2
iteration 3-2: next[0] = 0
iteration 3-3: next[0] = 3

It seems to me that somehow, during the execution of *strcpy(strtok_buffer, strtok_result);* the value of next[0] is altered. This boggles me. I have encountered similar results before, and that had to do with memory overlapping (term?), but I cannot see why this would occur here.

Any help is appreciated, I have stared myself blind trying to figure this out.

Notes:

Upvotes: 4

Views: 794

Answers (1)

Michael Burr
Michael Burr

Reputation: 340218

strtok_buffer[2] is not large enough to hold the tokens "A1", "B2", or "C3". Don't forget that strings need space for the terminating null character.

Upvotes: 5

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