export LD_LIBRARY_PATH=~/rsfitsio/target/debug

gcc -L ../target/debug -o testprog testprog.c -lrsfitsio

gcc -L ../target/debug -o cookbook cookbook.c -lrsfitsio

gcc -L ../target/debug -o speed speed.c -lrsfitsio

If C debug doesn't work, Cntrl+Shift+P -> Run Build Task

gcc -o print_c print_c.
rustc print_rs.rs