When working with strings in Arduino, there are several ways to compare them. One of the most useful functions is strcmp(), which belongs to the C standard library, cstringThis function allows you to compare two character strings in a direct way, returning a value that tells us whether the strings are equal or if there is any difference between them.
In Arduino, strings are commonly handled through objects of the class String, although it is also an option to work with character arrays, especially if we want to optimize resources or work with low-memory code. Let's delve into how to use the function correctly strcmp() and other alternatives that are also useful in this environment.
What is strcmp() and how does it work in Arduino?
The function strcmp() has a fairly simple behavior: it takes two character strings, compares them character by character, and returns a value based on that comparison. The method evaluates the ASCII values of the characters, which is important to keep in mind. The possible results of this comparison are as follows:
- If the strings are equal,
strcmp()bring back 0. - If the first character that differs has a lower ASCII value in the first string, the function will return a negative number.
- If the unmatched character in the first string is greater than 1, it will return a positive number.
A practical example of using the function strcmp() is to compare two strings that we enter or generate using other functions. For example, we can create a program that collects data from the user and, by comparing it with a stored string, validate whether the information is correct.
Important differences between strcmp() and other functions
When working with strings in Arduino, there are other alternatives to strcmp() that may best fit your needs. One of them is memcmp(), which performs a memory-level comparison, useful when we don't want to rely on a null terminator in our strings. Unlike strcmp(), which is designed to work with null-terminated strings, memcmp() simply compares a specific number of bytes.
Let's look at its basic syntax:
if (memcmp(payload, "cadena", longitud) == 0) { // Ejecuta la acción}Given its flexibility, it is a very useful option if you work with chunks of data or fixed-length messages that must be compared byte by byte.
Specific use cases: monitoring and comparing chains in real time
Imagine you are working on a project where you receive real-time information and you need to compare it with a specific value. The function strcmp() is a key tool in these types of situations. For example, if you are comparing data received from a sensor and you want to validate if it matches a predefined value, strcmp() will allow you to do this efficiently.
In this code snippet, we compare whether the value received from a pH sensor matches certain calibrated values:
if (strcmp(inputString, "CAL,4") == 0) { // Acción cuando se recibe el valor de calibración}This type of comparison is crucial in applications where data may vary and we must make decisions based on the results of the readings.
Other methods for working with strings
Apart from strcmp(), you can also use other functions within the Arduino ecosystem. The function compareTo, for example, is part of the class String and makes it easier to compare objects of that class. Although strcmp() It is more common in low-level implementations or with character arrays, compareTo It is useful if you are already working with objects String.
Here are some additional methods you can use:
- compareTo(): Compare two objects
Stringand returns a comparison value as instrcmp(). - equals (): Checks if two string objects are exactly equal, returning true or false.
Common problems and how to fix them
One of the most common mistakes when using strcmp() in Arduino is not making sure that strings are properly terminated with a \0 (null character). If the string is not properly terminated, the function will continue comparing in memory longer than you expect, which may result in unexpected errors or erratic behavior.
If you suspect that your strings are not terminated correctly, you can resort to solutions such as memcmp(), which does not rely on null to delimit the string, and allows you to specify a specific number of bytes to compare.
Another issue you might encounter is when comparing strings you may have received via serial input. You should always make sure to clean up and format the strings before attempting any comparison.
Full implementation example
To illustrate how these tools work in a real project, here is an example that combines string comparison with the function Serial.println() to display the results on the Arduino serial monitor:
#include <string.h> void setup() { Serial.begin(9600); char str1[] = "Hola"; char str2[] = "Hola"; int result = strcmp(str1, str2); if (result == 0) { Serial.println("Las cadenas son iguales"); } else if (result > 0) { Serial.println("La primera cadena es mayor"); } else { Serial.println("La segunda cadena es mayor"); } } void loop() { }This code compares two strings and displays the results on the monitor. It is a good example of the practical use of strcmp() in real Arduino applications to efficiently compare text strings.
In addition to comparison, you can use the output of strcmp() within conditional structures such as if to perform certain actions when strings match or not.
Optimization in projects with limited resources
As you may have noticed, the use of strcmp() and similar functions is a very efficient option when we have projects with memory limitations, which is quite common in Arduino projects. By using character arrays instead of objects String, we optimize memory consumption, which is essential when working on microcontrollers with little storage capacity.
Finally, it is important to note that in projects where sensors, interfaces or communication modules are used, it is essential to validate each data received to avoid errors in execution or undesired behavior.
All of the above, strcmp() It is a very versatile tool that adapts to multiple scenarios, from the simplest to much more complex applications where it is necessary to optimize resources and make decisions based on string comparisons.