81. Split a String Using Delimiter

#include <stdio.h>
#include <stdint.h>

void split_string(const char *str, char delimiter, char tokens[10][20], uint8_t *count) {
    uint8_t row = 0, col = 0;
    *count = 0;

    for (uint8_t i = 0; str[i] != '\0'; i++) {
        if (str[i] == delimiter) {
            if (col > 0) {
                tokens[row][col] = '\0';  // End current token
                row++;
                col = 0;
            }
        } else {
            if (col < 19) {
                tokens[row][col++] = str[i];
            }
        }
    }

    // Final token
    if (col > 0) {
        tokens[row][col] = '\0';
        row++;
    }

    *count = row;
}

int main() {
   char str[101];
   char delimiter;
   fgets(str, sizeof(str), stdin);
   scanf(" %c", &delimiter);

   // Remove newline
   uint8_t i = 0;
   while (str[i]) {
       if (str[i] == '\n') { str[i] = '\0'; break; }
       i++;
   }

   char tokens[10][20];
   uint8_t count = 0;

   split_string(str, delimiter, tokens, &count);

   for (uint8_t i = 0; i < count; i++) {
       printf("%s\n", tokens[i]);
   }

   return 0;
}

What is this about?

Simulate splitting a string on a delimiter without using strtok(), and store tokens manually in a 2D char array.

Why it matters in firmware?

• strtok() uses static memory and is not reentrant — not ideal in interrupt routines or multi-threaded environments
• Command parsers for UART/SPI/I2C shells need precise and safe tokenization
• Token buffers are often statically allocated in firmware

Solution Logic

• Loop through each character
• Copy characters into current token until delimiter 
• On delimiter, terminate current token and move to next row
• Handle the last token after loop