Why to Avoid printf in Embedded Systems

January 15, 2024 / By Sivanesh.

printf is a function in the C programming language that is used for formatted output. It is part of the standard input/output library, which is denoted by the header file stdio.h. The printf function allows you to display information on the console or other output devices in a formatted way.

The basic syntax of printf is:

printf(format_string, arguments);

– format_string: A string that specifies the format of the output. It may contain format specifiers like %d, %s, %f, etc.

– arguments: Values to be inserted into the format string based on the format specifiers.

Using printf in embedded systems can lead to several issues, including increased code size, execution time, and resource usage. Let’s explore these issues with a simple example. For this example, let’s consider a hypothetical embedded system with limited resources.

#include <stdio.h>

void initializeHardware() {
    // Code for initializing hardware
}
void mainLoop() {
    int sensorValue = 42;
    float temperature = 25.5;
    // Some processing code
    // Using printf for debugging
    printf("Sensor Value: %d, Temperature: %.2f\n", sensorValue, temperature);
    // More processing code
}

int main() {
    initializeHardware();
    while (1) {
        mainLoop();
    }
    return 0;
}

Code Size:

When you compile this code with a standard library that includes printf, the resulting binary may be significantly larger. In an embedded system with limited flash memory, this increase in code size can be a critical problem.

Execution Time:

The printf function, especially when dealing with floating-point numbers, can be computationally expensive. In embedded systems where real-time performance is crucial, using printf might introduce unacceptable delays.

Memory Usage:

The printf function relies on a substantial amount of memory, especially when supporting a variety of formatting options. In resource-constrained environments, this memory usage might be better utilised for other critical tasks.

Lack of Control:

printf is a general-purpose function designed for a wide range of applications. In embedded systems, you may need more control over how data is formatted and output. Using custom logging functions or simpler output mechanisms provides this control.

To address these issues, you could replace the printf statement with a custom logging function tailored to your needs. Here’s a modified example using a basic custom logging function:

#include <stdio.h>

void initializeHardware() {
    // Code for initializing hardware
}

void logData(int sensorValue, float temperature) {
    // Custom logging function implementation
    // Output the data in a way suitable for the embedded environment
}

void mainLoop() {
    int sensorValue = 42;
    float temperature = 25.5;

    // Some processing code

    // Using custom logging function for debugging
    logData(sensorValue, temperature);

    // More processing code
}

int main() {
    initializeHardware();

    while (1) {
        mainLoop();
    }

    return 0;
}

This custom logging function allows you to have more control over the format of the output, reduces code size, and potentially improves the execution time and resource usage for your embedded system.

Introduction – KAST Checker to detect printf in code

We understand the challenges that arise when using printf in embedded systems development. To assist fellow developers in addressing and resolving printf-related issues, we’ve created a custom KAST (Klocwork Abstract Syntax Tree) checker tailored for this purpose.

Key Benefits:

Precision Detection:

Our KAST checker is designed to precisely identify all instances of printf in your source code, ensuring thorough coverage and accuracy in issue detection.

Efficient Issue Resolution:

By pinpointing printf-related problems early in the development process, our tool empowers you to resolve issues efficiently, reducing the likelihood of runtime errors in embedded systems.

Customizable Rules:

Tailor the checker to your specific project needs. With customizable rules, you have the flexibility to focus on the aspects of printf usage that are most critical for your application.

Integration with Klocwork:

Seamlessly integrate our custom checker into your Klocwork environment, enhancing your static code analysis capabilities and promoting code quality within your embedded systems projects.

Download our KAST checker now and experience the benefits firsthand. Elevate your embedded systems development by proactively addressing printf-related issues, ensuring robust and reliable code.

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We value your feedback! Feel free to share your experiences with the tool, report any issues, or suggest improvements. Together, let’s optimize embedded systems code for peak performance.

Sample Screenshot,

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