Created
November 6, 2013 18:10
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hex string to byte array, C
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unsigned char* hexstr_to_char(const char* hexstr) | |
{ | |
size_t len = strlen(hexstr); | |
IF_ASSERT(len % 2 != 0) | |
return NULL; | |
size_t final_len = len / 2; | |
unsigned char* chrs = (unsigned char*)malloc((final_len+1) * sizeof(*chrs)); | |
for (size_t i=0, j=0; j<final_len; i+=2, j++) | |
chrs[j] = (hexstr[i] % 32 + 9) % 25 * 16 + (hexstr[i+1] % 32 + 9) % 25; | |
chrs[final_len] = '\0'; | |
return chrs; | |
} |
@guigarma This is pretty helpful. When checking if the string is valid hex it only checks for capital letters A-F (ASCII 65 - 70). If you use something like sprintf
to produce the hex string then the output will use lowercase letters and the function doesn't work. I added a small check to fix that.
int HexStringToBytes(const char *hexStr,
unsigned char *output,
unsigned int *outputLen)
{
size_t len = strlen(hexStr);
if (len % 2 != 0) {
return -1;
}
size_t finalLen = len / 2;
*outputLen = finalLen;
for (size_t inIdx = 0, outIdx = 0; outIdx < finalLen; inIdx += 2, outIdx++) {
if ((hexStr[inIdx] - 48) <= 9 && (hexStr[inIdx + 1] - 48) <= 9) {
goto convert;
} else {
if (((hexStr[inIdx] - 65) <= 5 && (hexStr[inIdx + 1] - 65) <= 5) || ((hexStr[inIdx] - 97) <= 5 && (hexStr[inIdx + 1] - 97) <= 5)) {
goto convert;
} else {
*outputLen = 0;
return -1;
}
}
convert:
output[outIdx] =
(hexStr[inIdx] % 32 + 9) % 25 * 16 + (hexStr[inIdx + 1] % 32 + 9) % 25;
}
output[finalLen] = '\0';
return 0;
}
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It is very nice, but it does not check if the hex string is an actual hex string (for example "3FZP"). Here is a version that does that, also without malloc (since some embedded systems does not implement it (like one I'm currently working with)). Code a little verbose in naming.