Save query in csv

hi, firt my name is Rio.
i need some help for source code in c. now i use cygwin and postgre to make a program based on c.
could you help me in code, how to save query result in file. i want to make file *.csv(comma separeted value).
i have found a source code based on c to parse the file from *.csv. but i have not found source code to make file *.csv (its means that the result of query in postgre).
for helping, thhank so muc

Rio junior
Indonesia