Byte text file to array

Question

I'm trying to display a bitmap on gLCD 128x64, I stored the bitmap into txt file 1.txt in a SD card this is a part of bit map as following:

0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x80, 0xC0, 0xC0, 0xC0, 0xC0, 0xC0, 0xC0, 0xC0, 0xC0, 0xC0, 0x80, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00.......

I want to convert the content of this text into array: Unsigned char logo[] with making a split on ",".

Any help please

Answer 1

The most efficient way is to read the file byte-by-byte into a small character array until you get a comma or the end of file - ignoring any characters that aren't of interest (line feeds, etc).

Then for each chunk that you read you then convert it to an integer.

For example (untested):

char temp[5] = {0}; // should be more than enough
int pos = 0;
int bno = 0;
const char *hexchars = "0123456789abcdefABCDEFx";
while ((int ch = myFile.read()) >= 0) {
 if (ch == ',') { // We found a comma
 logo[bno++] = strtoul(temp, NULL, 16); // Base 16 conversion
 pos = 0;
 temp[0] = 0;
 } else if (strchr(hexchars, ch) != NULL) {
 if (pos < 4) {
 temp[pos++] = ch;
 temp[pos] = 0;
 }
 }
}

Of course, you have to know how big the logo array has to be beforehand.

One does, though, have to ask "Why are you storing a graphical logo as a textual representation of binary data" in the first place? It would be far easier to just store it as a simple binary file and read the data directly into the logo array with a single File::read(void *buf, size_t nbyte); function call. Using text as an intermediate format is both wasteful and needlessly increases complexity massively.