Embedded Prep

Compare firmware version strings in C : In embedded systems development, firmware updates are crucial for fixing bugs, improving performance, or adding new features. A common challenge developers face is comparing two firmware version strings in C to decide whether an upgrade or downgrade is required.

For example, you might want to check if version “1.2.10” is newer than “1.2.9”. At first glance, this looks like a simple string comparison—but in practice, you need to handle version numbers numerically, not lexicographically.

Compare firmware version strings in C this article, we will:

• Understand the basics of firmware version strings
• Learn why direct string comparison fails
• Write a C program to compare version strings properly
• Explore practical use cases in embedded software development

What is a Firmware Version String?

A firmware version string is a sequence that represents the version of your software. Common formats include:

• "1.0.0" → (major.minor.patch)
• "2.5" → (major.minor)
• "3.10.7-beta" → (with suffix)

Each number (major, minor, patch) carries meaning:

• Major version: Big changes, possibly breaking compatibility.
• Minor version: New features, still backward compatible.
• Patch version: Small fixes or improvements.

Why Simple String Comparison Fails

Let’s say we compare “1.10” and “1.2” as strings.

strcmp("1.10", "1.2");  

Here, "1.10" would be considered smaller than "1.2" because strcmp compares character by character ('1' == '1', then '0' < '2').

But in reality:

• 1.10 (ten) is greater than 1.2 (two).

So, we need numeric comparison.

Pseudocode: Compare Two Firmware Version Strings

How the Pseudocode Works

1. Iterate through both version strings simultaneously.
2. Extract numbers between dots (.) and convert them to integers.
3. Compare numbers one by one:
   • If a number in version1 is greater → version1 is newer.
   • If a number in version2 is greater → version2 is newer.
   • If equal → continue.
4. Handle versions of different lengths by treating missing numbers as 0.
5. Return 0 if all numbers are equal.

This pseudocode is optimized for embedded systems logic and avoids string splitting with extra memory allocation.

C Program to Compare Firmware Version Strings

Here’s a beginner-friendly C program that compares two version strings correctly:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// Function to compare two firmware version strings
int compareVersions(const char *v1, const char *v2) {
    // Create copies since strtok modifies strings
    char *ver1 = strdup(v1);
    char *ver2 = strdup(v2);

    char *token1 = strtok(ver1, ".");
    char *token2 = strtok(ver2, ".");

    while (token1 != NULL || token2 != NULL) {
        int num1 = (token1 != NULL) ? atoi(token1) : 0;
        int num2 = (token2 != NULL) ? atoi(token2) : 0;

        if (num1 > num2) {
            free(ver1); free(ver2);
            return 1;  // v1 is greater
        } else if (num1 < num2) {
            free(ver1); free(ver2);
            return -1; // v2 is greater
        }

        token1 = (token1 != NULL) ? strtok(NULL, ".") : NULL;
        token2 = (token2 != NULL) ? strtok(NULL, ".") : NULL;
    }

    free(ver1);
    free(ver2);
    return 0; // Both versions are equal
}

int main() {
    const char *v1 = "1.2.10";
    const char *v2 = "1.2.9";

    int result = compareVersions(v1, v2);

    if (result == 0) {
        printf("Both versions are equal.\n");
    } else if (result > 0) {
        printf("Version %s is newer than %s.\n", v1, v2);
    } else {
        printf("Version %s is newer than %s.\n", v2, v1);
    }

    return 0;
}

Explanation of the Code: Compare version numbers in embedded systems

1. Splitting the version string:
   • We use strtok with "." as a delimiter to separate numbers like "1", "2", "10".
2. Converting to integers:
   • Each token is converted using atoi().
   • "10" becomes 10 (so "1.10" > "1.2").
3. Comparison logic:
   • If one number is greater, we immediately return the result.
   • If equal, we move to the next part.
   • If lengths differ (e.g., "1.2" vs "1.2.0.0"), missing parts are treated as 0.

Example Output of C code for firmware version management

For input:

v1 = "1.2.10"
v2 = "1.2.9"

Output:

Version 1.2.10 is newer than 1.2.9.

Optimized Firmware Version Comparison in C (No strtok / No strdup)

When writing firmware for resource-constrained embedded devices, we must minimize memory usage and avoid dynamic allocations like malloc, strdup, or even temporary token buffers.

Instead of splitting the version string, we can parse it character by character, extracting numbers on the fly.

Optimized C Code of Numeric comparison of version strings in C

#include <stdio.h>
#include <ctype.h>

// Function to extract the next integer from version string
int getNextNumber(const char **str) {
    int num = 0;

    // Parse until '.' or end of string
    while (**str && **str != '.') {
        if (isdigit(**str)) {
            num = num * 10 + (**str - '0');
        }
        (*str)++;
    }

    // Skip the '.' character
    if (**str == '.') {
        (*str)++;
    }

    return num;
}

// Compare two firmware version strings
int compareVersions(const char *v1, const char *v2) {
    while (*v1 || *v2) {
        int num1 = getNextNumber(&v1);
        int num2 = getNextNumber(&v2);

        if (num1 > num2) return 1;   // v1 is greater
        if (num1 < num2) return -1;  // v2 is greater
    }
    return 0; // Versions are equal
}

int main() {
    const char *v1 = "2.10.3";
    const char *v2 = "2.9.15";

    int result = compareVersions(v1, v2);

    if (result == 0) {
        printf("Both versions are equal.\n");
    } else if (result > 0) {
        printf("Version %s is newer than %s.\n", v1, v2);
    } else {
        printf("Version %s is newer than %s.\n", v2, v1);
    }

    return 0;
}

How Compare software version strings in C Works

1. getNextNumber function
   • Reads characters until a . or \0 (end of string).
   • Converts digits into an integer ("15" → 15).
   • Skips the dot (.) and prepares for the next segment.
2. compareVersions function
   • Loops until both strings are fully read.
   • Extracts one integer from each version string.
   • Compares them immediately.
   • If equal, continues to the next part.
   • If different, returns the comparison result.
3. No extra memory
   • Works directly on the input strings.
   • No heap allocation, no strdup, no strtok.

C program to compare version numbers Example Run

Input:

v1 = "2.10.3"
v2 = "2.9.15"

Output:

Version 2.10.3 is newer than 2.9.15.

Advantages for Embedded Systems Compare version numbers in embedded systems

• No dynamic memory allocation (safe for microcontrollers).
• Faster execution since it parses directly.
• Smaller memory footprint.
• Works even if versions have different lengths ("1.2" vs "1.2.0.0").

Real-World Use Cases of Compare version numbers in embedded systems

• Over-the-Air (OTA) Updates: Check if the device needs a firmware upgrade.
• Bootloaders: Ensure only newer firmware is flashed.
• Diagnostics Tools: Display correct version hierarchy.
• Version Management: Maintain compatibility in embedded systems.

Final Thoughts of C code for firmware version management

Comparing firmware version strings in C is more than a simple string check—it requires numeric comparison to handle multi-digit versions correctly. By splitting the string, converting to integers, and comparing each part step by step, you can build a robust firmware version checker for your embedded systems projects.

Frequently Asked Questions (FAQ) | Firmware version comparison in C language

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