Is there a way to find all the functions used in a c program?

I have the source code for a huge (exaggerated) c program with multiple files. I was hoping if there was any way to find all the functions (both standard and builtin) used (both declared and called) in the program. I know I can compile it and track the function and system calls using tools like ltrace and strace, by redirecting the output to a file first and then using grep to select the function calls. Or I can use regex on shell on all the files, but I don't know regex (yet). So does any one know a tool that could help me to quickly find all the functions called and declared in a c program?

Solution

Check if this helps, comments in code:

#!/bin/bash

# For each .c in the current path (recursive)
for f in $(find . -name '*.c'); do
    # Extract the functions and his location with aux-info
    # Send the results to output.info
    # Send errors to /dev/null
    gcc -aux-info output.info $f 2>/dev/null
    # Extract function names from output.info excluding std headers and comments
    grep -Ev "/usr|compiled from" output.info
done
# Remove output.info
rm output.info

Since it seems that you are trying to extract your own code following a pattern: type function(params), you can avoid using gcc -aux-info, try the following:

#!/bin/bash

# For each .c in the current path (recursive)
for f in $(find . -name '*.c'); do
    # Extract the lines starting with a letter or underscore
    #                 and ending with ')' or '{' or '}' ignoring trailing spaces
    grep --with-filename --line-number --color '^[a-z|A-Z|_].*[)|{|} ]$' $f
done

Another way combining readelf and awk, notice that in this case you need to provide the name of the program/binary instead of the source files:

# Column 3 != 0 and Column 4 = "FUNC" and Column 8 not starting with _
readelf -sW your_program | awk '$3 != 0 && $4 == "FUNC" && $8 !~ /^ ?_/ {print $8}'