Unable to convert number to uint8_t using sscanf

RE: Unable to convert number to uint8_t using sscanf

rgujju — Wed, 30 Jan 2019 15:54:55 GMT

No, %hhu does not work. What library can i use? I am using the standard library with gcc Makefile. Do i need to add some compiler flags or something?

RE: Unable to convert number to uint8_t using sscanf

hmolesworth — Tue, 29 Jan 2019 18:57:15 GMT

I use the following for 8-bit hex; %c probably works for 8-bit character. A lot depends on the settingf for the scanf library your compiler is using; I use IAR with full library (Use the full configuration of the C/C++ runtime library. Full locale interface, C locale, file descriptor support, multibytes in printf and scanf, and hex floats in strtod). If the IDE/compiler you use doesn't support some things, it is also possible to use your own sscanf by searching on the web for an example source which can be edited to be minimal.

// 8-bit unsigned hex byte %hX:
   uint8_t AccRegisters[ACC_REGISTER_MAX_COUNT+1] = {0x40|0x38, 0x2A, 0x00, 0x25, 0x30, 0x30, 0x65};
   numValues = sscanf(p_data,"%hX %hX %hX %hX %hX %hX %hX",
                      &RequestStartIndex,                // Starting register index
                      &AccRequestRegisters[0],           //  0
                      &AccRequestRegisters[1],           //  1
                      &AccRequestRegisters[2],           //  2
                      &AccRequestRegisters[3],           //  3
                      &AccRequestRegisters[4],           //  4
                      &AccRequestRegisters[5]            //  5
                         );

// 16-bit unsigned integer %hu:
   uint16_t Option;
   sscanf(p_data,"%hu", &Option);

Also %hhu might work, depending on your library ..

RE: Unable to convert number to uint8_t using sscanf

rgujju — Tue, 29 Jan 2019 17:34:15 GMT

then what format specifier should i use to convert to 1 byte? I have tried with %c as well, and it doesnt seem to work.

RE: Unable to convert number to uint8_t using sscanf

Turbo J — Mon, 28 Jan 2019 19:19:19 GMT

The sscanf() function requires that the destination for the "%d" conversion is 4 bytes - sizeof(int) wide. This will overwrite adjacent fields in your struct of uint8_t values.

Workaround: Use temporary int variables on the stack.