I need to get the first item from an string arrays in C, this is my code:
#include <stdio.h>
#include <string.h>
int main() {
char *codes[16] = {
"VVVV", "VVVB", "VVBV", "VVBB", "VBVV", "VBVB", "VBBV", "VBBB",
"BVVV", "BVVB", "BVBV", "BVBB", "BBVV", "BBVB", "BBBV", "BBBB"
};
char code[4];
int ret = 0;
int j = 0;
printf("Enter code to search: ");
scanf("%s", code);
for (j = 0; j < 16; j++) {
printf("\ncode to search is: %s, j value: %d, codes[j]: %s",
code, j, codes[j]);
ret = strcmp(code, codes[j]);
if (ret == 0) {
printf("\nValue of index: %d\n", j);
}
}
}
When I enter the first code to search (VVVV
) I get a void value in position 0, and It doesn't return the index 0. Another values works but the first doesn't.
This is the output:
Enter code to search: VVVV
code to search is: VVVV, j value: 0, codes[j]:
code to search is: VVVV, j value: 1, codes[j]: VVVB
code to search is: VVVV, j value: 2, codes[j]: VVBV
code to search is: VVVV, j value: 3, codes[j]: VVBB
code to search is: VVVV, j value: 4, codes[j]: VBVV
code to search is: VVVV, j value: 5, codes[j]: VBVB
code to search is: VVVV, j value: 6, codes[j]: VBBV
code to search is: VVVV, j value: 7, codes[j]: VBBB
code to search is: VVVV, j value: 8, codes[j]: BVVV
code to search is: VVVV, j value: 9, codes[j]: BVVB
code to search is: VVVV, j value: 10, codes[j]: BVBV
code to search is: VVVV, j value: 11, codes[j]: BVBB
code to search is: VVVV, j value: 12, codes[j]: BBVV
code to search is: VVVV, j value: 13, codes[j]: BBVB
code to search is: VVVV, j value: 14, codes[j]: BBBV
code to search is: VVVV, j value: 15, codes[j]: BBBB
What could be wrong?
Your code has a buffer overflow, which is a very dangerous kind of undefined behaviour.
The following line
char code[4];
declares an array of char that can hold up to 3 characters plus a null-terminator character, which add up to 4 characters total. This is because C strings are null-terminated.
When you attempt to scan a 4 character string (don't forget the 5th \0
that's added automatically) into a 3 character buffer (plus the 4th \0
), your code overflows. Therefore, you need to change the line above to
char code[5];
That said, your code is far from being trouble-safe. And yes, I mean that scanf()
call. I suggest you read this post as it explains the pitfalls of that function, and provides alternative solutions.
Here is a better version of your code:
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
int main(void)
{
char *codes[] = { // Let your array be flexible in case you want to add to it later.
"VVVV", "VVVB", "VVBV", "VVBB",
"VBVV", "VBVB", "VBBV", "VBBB",
"BVVV", "BVVB", "BVBV", "BVBB",
"BBVV", "BBVB", "BBBV", "BBBB"
};
// Computes the size (number of items) of an array object.
// Doesn't work for pointers to arrays.
// Also, use size_t as it's the appropriate type for sizes.
size_t ncodes = sizeof(codes) / sizeof(codes[0]);
char code[5]; // <-- 4 characters + \0
printf("Enter code to search: ");
if (scanf(" %4[^\n]", code) != 1) {
printf("Error: scanf() failed.\n");
return 1;
}
bool found = false;
for(size_t j = 0; j < ncodes; ++j) {
if (strcmp(code, codes[j]) == 0) {
printf("Code found at index: %zu\n", j);
found = true;
break; // Stop looping when you find the first occurence
}
}
if (!found) {
printf("Code %s not found.\n", code);
}
}