This is one of those, "I know there is a better way", questions.
The below code is from a larger project I am working on, and the helper function to convert a hex value to a binary string is buried deep in the code.
Essentially, I want to make sure that the char array pointed to by *return_string has sufficient space for the binary string generated by the function.
As it stands, if I don't allocate enough memory, I get a SIGABRT. It would be far more elegant if I just returned -1.
The research I have done tells me that what I am trying to do is a bit tricky, since there is really no way to bounds check an empty array via its pointer.
For reasons that I don't understand, if I use the common macro:
#define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0]))
On *return_string, I always get the same value. I am new to C - I am sure I am missing something elementary here.
Anyway, here's the code. What do you all recommend? Thank you!
(FYI - I know that as written, I do not have enough memory allocated)
(FYI - I also know that this is not the fastest implementation of a hex to binary conversion. O(n) is good enough for this particular application)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int hex_string_to_bin_string(char *return_string, size_t bin_length, const char *input);
int main(int argc, const char * argv[]) {
char return_string1[12];
char return_string2[12];
char return_string3[12];
char input1[8] = "0x4708";
char input2[8] = "4708";
char bad_input[8] = "47Q8";
fprintf(stderr, "answer should be:\t\t\t 0100011100001000\n");
//test string 1
if(hex_string_to_bin_string(return_string1, 16, input1) < 0 ) {
fprintf(stderr, "FAILED return string 1\n");
} else {
fprintf(stderr, "return string 1:\t\t\t %s\n", return_string1);
}
//test string 2
if(hex_string_to_bin_string(return_string2, 16, input2) < 0 ) {
fprintf(stderr, "FAILED return string 2\n");
} else {
fprintf(stderr, "return string 2:\t\t\t %s\n", return_string2);
}
//test bad input
if(hex_string_to_bin_string(return_string3, 16, bad_input) < 0) {
fprintf(stderr, "PASSED bad character test\n");
}
else {
fprintf(stderr, "FAILED bad character test\n");
}
return 0;
}
int hex_string_to_bin_string(char *return_string, size_t bin_length, const char *input) {
/*
0 - 0000
1 - 0001
2 - 0010
3 - 0011
4 - 0100
5 - 0101
6 - 0110
7 - 0111
8 - 1000
9 - 1001
A - 1010
B - 1011
C - 1100
D - 1101
E - 1110
F - 1111
*/
//check input to make sure length is good
if(strlen(input) == 0 ) {
return -1;
}
//check for leading '0x' and strip if necessary
if(input[0] == '0' && input[1] == 'x') {
input += 2;
}
//loop through input and replace
int i;
char bits[5];
for(i=0; i<strlen(input); i++) {
switch(input[i]) {
case '0': {
if( snprintf(bits, sizeof(bits), "0000") < 0) {
return -1;
}
break;
}
case '1': {
if( snprintf(bits, sizeof(bits), "0001") < 0) {
return -1;
}
break;
}
case '2': {
if( snprintf(bits, sizeof(bits), "0010") < 0) {
return -1;
}
break;
}
case '3': {
if( snprintf(bits, sizeof(bits), "0011") < 0) {
return -1;
}
break;
}
case '4': {
if( snprintf(bits, sizeof(bits), "0100") < 0) {
return -1;
}
break;
}
case '5': {
if( snprintf(bits, sizeof(bits), "0101") < 0) {
return -1;
}
break;
}
case '6': {
if( snprintf(bits, sizeof(bits), "0110") < 0) {
return -1;
}
break;
}
case '7': {
if( snprintf(bits, sizeof(bits), "0111") < 0) {
return -1;
}
break;
}
case '8': {
if( snprintf(bits, sizeof(bits), "1000") < 0) {
return -1;
}
break;
}
case '9': {
if( snprintf(bits, sizeof(bits), "1001") < 0) {
return -1;
}
break;
}
case 'A': {
if( snprintf(bits, sizeof(bits), "1010") < 0) {
return -1;
}
break;
}
case 'B': {
if( snprintf(bits, sizeof(bits), "1011") < 0) {
return -1;
}
break;
}
case 'C': {
if( snprintf(bits, sizeof(bits), "1100") < 0) {
return -1;
}
break;
}
case 'D': {
if( snprintf(bits, sizeof(bits), "1101") < 0) {
return -1;
}
break;
}
case 'E': {
if( snprintf(bits, sizeof(bits), "1110") < 0) {
return -1;
}
break;
}
case 'F': {
if( snprintf(bits, sizeof(bits), "1111") < 0) {
return -1;
}
break;
}
default: {
return -1;
}
}
if(i == 0) {
snprintf(return_string, bin_length+1, "%s", bits);
}
else {
snprintf(return_string, bin_length+1, "%s%s", return_string, bits);
}
}
return 0;
}
