Concatenate using Sprintf %d%c (3 digit number + 1 Character)

Projects Programming
1

Hi,

I am trying to convert 110 + A (%d,%c) using sprinf but results are weird in serial monitor. (getting 10734���?���) instead of 110A.

using ESP32 Dev Kit V1 Hardware

int k = 0;
int digit3 = 110;
char alphabet[3] = {'A','B','C'};
char result[5];
sprintf(result, "%d,%c", digit3, alphabet[k]); // generate cstring "110A"
Serial.println(result);

what could be wrong in above code ?

2

Please post a small but complete sketch that shows the problem. How are digit3 and k declared, for instance ?

3

"110,A" that's 5 bytes for the text and one extra byte for the trailing nul char. so your result array is too small.

2 Likes
4

Set the baudrate of the Serial Monitor to the same baudrate as in your sketch.

The buffer for the result is too small. A "%d" can be 6 characters for a 16 bit integer or 11 for a 32 bit integer, plus 1 for the comma, plus 1 for "%c", plus a zero-terminator. So 14 is the absolute minimum. I could have calculated it wrong, so can you make it 20 ?

char result[20];
1 Like
5

you should use snprintf() to not overflow

6

Noted. Thanks

7

Of course, snprintf() is only as good as the parameters that you pass it

8

yes, that too. Your answer in post#2 is still to the point. OP should not post snippets (Snippets R Us!)

9

sorry for mis-out. i have edited my post for incomplete information.

10

I hope you are not using 6 bytes for the buffer now :scream:

11

unless you're very tight on memory, just define a char array with more than enough length (e.g. 80) as a global for use in these situations

12

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