Stdio


The standard I/O library simplifies the use of files
fopen(3), fclose(3), fread(3), fwrite(3), fseek(3), ...
popen(3) calls an external command
fdopen(3) promotes an fd into a file pointer
fscanf(3), fprintf(3), fgets(3), puts(3)

Obviously, stdio has disadvantages too:
select(2) and poll(2) will just not work
non-blocking files are a real pain
scanf(3) can block unexpectedly