Which Branch Should I Download?

[Curry-Icecream]

Currently, Im using raspberry pi 5, should I download v2.1 or the master branch?

Currently what I'm doing is I've downloaded the master branch and did what have been told in ReadMe file, then put the bin, include and lib into /usr/local/"corresponding dir", then I used Make All in geany and tried to compile the example code (the one about toggle line), and it did say pin 17 is active and inactive consecutively, but my led connected to pin 17 didn't do anything.

If I build instead of Make, then it will say undefined to reference to something.

[brgl]

Currently, Im using raspberry pi 5, should I download v2.1 or the master branch?

You should typically use the latest stable release which is now v2.1.

Currently what I'm doing is I've downloaded the master branch and did what have been told in ReadMe file, then put the bin, include and lib into /usr/local/"corresponding dir", then I used Make All in geany and tried to compile the example code (the one about toggle line), and it did say pin 17 is active and inactive consecutively, but my led connected to pin 17 didn't do anything.

This is way too little information to help. When submitting a bug report you need to give developers as much info as possible. Exact commands you run, program output, environment etc.

If I build instead of Make, then it will say undefined to reference to something.

Same as above. I have no idea what undefined reference to something means.

[Curry-Icecream]

Thanks for the reply.
I have re-downloaded the library v2.1.x and tried to build "toggle_line_value.c" on geany and it gives me the following message:

gcc -Wall -o "toggle_line_value" "toggle_line_value.c" -lgpiod (in directory: /home/uobgip1/project/libgpiod/examples)
/usr/bin/ld: /tmp/cc3Gekjp.o: in function request_output_line': toggle_line_value.c:(.text+0x40): undefined reference to gpiod_line_settings_new'
/usr/bin/ld: toggle_line_value.c:(.text+0x5c): undefined reference to gpiod_line_settings_set_direction' /usr/bin/ld: toggle_line_value.c:(.text+0x68): undefined reference to gpiod_line_settings_set_output_value'
/usr/bin/ld: toggle_line_value.c:(.text+0x6c): undefined reference to gpiod_line_config_new' /usr/bin/ld: toggle_line_value.c:(.text+0x94): undefined reference to gpiod_line_config_add_line_settings'
/usr/bin/ld: toggle_line_value.c:(.text+0xb4): undefined reference to gpiod_request_config_new' /usr/bin/ld: toggle_line_value.c:(.text+0xd0): undefined reference to gpiod_request_config_set_consumer'
/usr/bin/ld: toggle_line_value.c:(.text+0xe0): undefined reference to gpiod_chip_request_lines' /usr/bin/ld: toggle_line_value.c:(.text+0xec): undefined reference to gpiod_request_config_free'
/usr/bin/ld: toggle_line_value.c:(.text+0x104): undefined reference to gpiod_line_config_free' /usr/bin/ld: toggle_line_value.c:(.text+0x114): undefined reference to gpiod_line_settings_free'
/usr/bin/ld: /tmp/cc3Gekjp.o: in function main': toggle_line_value.c:(.text+0x274): undefined reference to gpiod_line_request_set_value'
collect2: error: ld returned 1 exit status
Compilation failed.

[brgl]

The project - as per README - is built using autotools. Please use them as I don't support any other way of doing it.

[Curry-Icecream]

So if I choose Make all, then I can compile the code and the terminal would write:
17=Active
17=Inactive
17=Active

I have connected a led light to gpio 17, but it doesn't turn on when 17=Active.
The only thing I have changed is static const unsigned int line_offset = 17;, the other things are same as the example code "toggle_line_value.c"

[brgl]

This is still not enough information. Run the program through strace and post the output here.