CCS/TM4C129XNCZAD: sprintf problem with parameters

Hello Davide,

Float printing with functions like sprintf aren't always supported by the library used to include the sprintf function. You would first need to see if your sprintf function even supports what you are attempting to do.

The topic of printing floats came up last week and I addressed it for one user in this post with a different method, you may find it helpful: https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/p/663530/2438264#2438264

Also in another post, the user solved an issue with sprintf (which did support floating points) by increasing his stack size: https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/t/199796

In addition to Ralph's very good suggestions:

1. If available with your compiler toolchain, consider using snprintf() rather than sprintf(). With snprintf() you must provide the size of the buffer. Because it "knows" the size of the buffer, snprintf() function will not overrun the buffer and the resulting string will always be null-terminated. In the worst case scenario, the resulting string is truncated to fit within the buffer, and you can detect this condition by checking the return value of snprintf(). With the older sprintf() which does not "know" the buffer size, there is the possibility of overrunning that buffer and corrupting other memory in use by your program. The snprintf() function is available with most reasonably modern compilers.

2. I am not sure what output string you expected, but the format string you want is probably "%0.6f" (notice the decimal point). This will format your result to 6 decimal places.

Example using snprintf():

char mystring[20];

float myfloat = 1.2f;

snprintf(mystring, sizeof(mystring), "%0.6f", myfloat);

mystring should now contain "1.200000"

Note that if you pass a string buffer to one of your own functions which then passes it to snprintf(), you will also need to pass the size to your own function:

void myfunction(char * resultString, size_t sizeOfResultString, float floatValue)

{

snprintf(resultString, sizeOfResultString, "%0.6f", floatValue);

}

Do not make this mistake:

void myfunction(char * resultString, float floatValue)

{

snprintf(resultString, sizeof(resultString), "%0.6f", floatValue); // <--- WRONG!!

}

(The mistake here is that you would pass the size of the pointer to resultString, not the size of the buffer pointed-to by resultString.)

thanks for your message, answering to your point, i have already tryed the snprintf function but i get the same result, so i used it to truncate the conversion in this way

char mystring[6 + 1]; // + 1 for the terminating ascii null character

float myfloat = 123.456789;

snprintf(mystring, sizeof(mystring), "%06f", myfloat);

so the string will be actually truncated at 6 character, so mystring will contain "123.45\0" because i want a 6 characters length string and not 6 decimal.

i have also tryed to use a pointer char variable and get the dimension with the malloc but i don't know if it's possible with the microcontroller, i usually develop windows software and not micro software.