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In this tutorial, we will discuss strcpy()copying a string from one variable to another using the function in Arduino.

Arduino strcpy()Functions

strcpy()The function can copy a string containing null characters from one variable to another. strcpy()The basic syntax of the function is as follows.

output = strcpy(dest, source);

strcpy()The first input to the function should be of data type char and the second input should be of data type const char. The function returns the copied string as a string.

If the destination size exceeds the source size, strcpy()the function will also add a NUL character as a terminator in the destination string. If the destination string already stores a string, the previous string will be overwritten by the new string.

For example, let us define a string and strcpy()copy it into another variable using the function. See the code below.

void setup() {
  const char* source = "Hello World";
  char destination[17];
  Serial.begin(9600);
  strcpy(destination, source);
  Serial.println(destination);
}
void loop() {}

Output:

Hello World

In the above code, we use the Arduino's serial monitor to print the string, which is stored in a destinationvariable. destinationThe length of the variable should be large enough to hold the entire sourcestring.

If the length is smaller than sourcestring, the result will be altered and strcpy()the function will have undefined behavior.

Since sourcethe and destinationstrings are of different sizes, strcpy()the function will overflow, causing problems in your code. The Arduino will not display an error due to overflow, and it may take a while to figure out what the problem is.

For example, let's destinationchange the size of the variable to 5, which is in the above code 17, and then check the result. See the code below.

void setup() {
  const char* source = "Hello World";
  char destination[5];
  Serial.begin(9600);
  strcpy(destination, source);
  Serial.println(destination);
}
void loop() {}

Output:

Èõüÿ

As we can see in the above output, the result has changed because destinationthe size of the variable is less than sourcethe size of the variable. To get good results, we have to make sure that destinationthe size of the variable is greater than sourcethe size of the variable.

We can use strcpy()a length-restricted version of the function, i.e. strncpy()the strncpy()function also sourcecopies the string to destinationthe variable, but it also takes the length of the destination as input.

The function writes NUL characters to fill the remaining space of string only when it sourceencounters a NUL character from string . If string does not have a NUL character, the string will not end with a NUL character.strncpy()destinationsourcedestination

For example, let's strncpy()repeat the above example using the function. See the code below.

void setup() {
  const char* source = "Hello World";
  char destination[5];
  Serial.begin(9600);
  strncpy(destination, source, sizeof(destination));
  Serial.println(destination);
}
void loop() {}

Output:

Hello

The output of this example contains sourcethe first 5 characters of . So, if we use strncpy()the function, we don't have to worry about overflow of the function because strncpy()it will destinationcopy sourcethe number of characters of according to the size of .

This function is also useful when we do not want to copy the entire string but only want to copy a few characters from the source to the destination. The strcpy()and strncpy()functions also return the copied string of char data type.

strcpy()There is another length-restricted version of the function, strlcpy()the function. strlcpy()The function is identical to strncpy()the function, except that strlcpy()the output of the function is the length of the source string.

Unlike strncpy()the function, strlcpy()the function does not write multiple NUL characters to fill destinationthe remaining space of the string, it only writes a single NUL character destinationto the string. destinationThe string will always strlcpy()be terminated with a single NUL character using the function.

destinationThe characters stored in the string will also include the NUL character. For example, if destinationthe size of the string is 5, we can only copy four characters in it due to the NUL character.

So we have to destinationincrease the size of the string to 6 to copy 5 characters into it. However, this is not the case with the strcpy()and strncpy()functions, they add a NUL character only when destinationthe size of the string is greater than sourcethe size of the string.

For example, let's strlcpy()repeat the above example using the function. See the code below.

void setup() {
  const char* source = "Hello World";
  char destination[5];
  Serial.begin(9600);
  strlcpy(destination, source, sizeof(destination));
  Serial.println(destination);
}
void loop() {}

Output:

Hell

As we can see in the output, four characters of the string have been copied even though destinationthe size is 5. This is because the function still looks at the end of the string.sourcedestinationstrlcpy()destination