Having issues while using %s

Question

I am working on a project in which I extract data received from GPS and save it in array named rx_data_buffer:

uint8_t rx_data_buffer[84] = {0};

The result I get is as below(see rx_data_buffer) : enter image description here

Then I extract the data from rx_data_buffer in following arrays:

uint8_t lattitude[10] = {0};
uint8_t longitude[10] = {0};
uint8_t altitude[5] ={0};

The data is extracted as follows:

for (uint8_t i =0; i < 10; i++)
{
  lattitude[i] = rx_data_buffer[i+17];
}
for (uint8_t j =0; j < 10; j++)
{
  longitude[j] = rx_data_buffer[j+31];
}
for (uint8_t k =0; k < 5; k++)
{
  altitude[k] = rx_data_buffer[k+56];
}

The results are as follows:

enter image description here

Till here everything is working fine but when I put the latitude, longitude and altitude data in an array using %s for the purpose of saving them in SD card as follow:

snprintf(mystring, sizeof(mystring), "\n%.2f,%.2f,%.2f,%.2f,%.2f,%.2f,%.2f,%.2f,%.2f,%d,%s,%s,%s",           readAccelerometer(X_AXIS),readAccelerometer(Y_AXIS),readAccelerometer(Z_AXIS),readGyro(X_AXIS),          readGyro(Y_AXIS),readGyro(Z_AXIS),readMagnetometer(X_AXIS),readMagnetometer(Y_AXIS),         readMagnetometer(Z_AXIS),heart_rate,longitude,lattitude,altitude);

I get the longitude and altitude values fine but am getting wrong latitude value in a sense that it show both the values combine as shown below:enter image description here.

What can be the issue?

Answer 1

In order to be used as strings, the arrays need a null terminator. Since you are initializing the arrays to zero, the simplest solution is to make them one larger than you need. eg:

uint8_t lattitude[11] = {0};
uint8_t longitude[11] = {0};
uint8_t altitude[6] ={0};

As long as you never write over the last element in the array, it will remain '\0' and you can use the string functions.