Best way to handle delimited files

Reusable for a function like the one you describe means several things:

• Doesn't assume the input is valid.
• Uses sane defaults.
• Prevents buffer overruns.
• Returns some indication of success or failure.

In your case:

#define BASE_PATH "/path/to/wherever"
bool build_path(char *dest, size_t size, char *subdir, char *filename)
{
    // Don't assume the input is valid
    if ( (dest == NULL) || (size < 1) || (filename == NULL) ) {
        return false;
    }

    // Make no subdir work  (sane default behavior)
    if ( subdir == NULL ) {
        subdir = "";
    }

    // Prevent buffer overruns by using a safe formatting function
    size_t stored = snprintf(dest, size, BASE_PATH "/%s/%s", subdir, filename);

    // Returns success (true) if the path fit the buffer
    return ((stored+1) <= size);
}


char fullpath[PATH_MAX];
if ( ! build_path(fullpath, sizeof(fullpath), "foo/bar", "baz") ) {
   // Handle error
}

The only thing I see inelegant about your implementation is intertwining the file listing work, the zip file opening/closing work, and the counting work. (Do you have another issue with it?)

Solution 1: Use Java's try-with-resources block to automate the file closing work thanks to ZipFile being AutoCloseable:

...
try (ZipFile zf = new ZipFile(file) {
  numberOfFilesInAllZipArchives += zf.size();
}
...

Solution 2: In Groovy, separate out the file listing work (and add filename filtering):

import java.util.zip.ZipFile

def dir = new File('Downloads')
def num = 0
dir.eachFileMatch(~/.*\.zip/) { f ->
    def z = new ZipFile(f)
    num += z.size()
    z.close()
}
println num

Solution 3: Also separate ZipFile open/closing work using Groovy's "with" idiom, adding a zipFileWith(closure) method to the class File:

import java.util.zip.ZipFile

File.metaClass.zipFileWith = { closure ->
    def zf = new ZipFile(delegate)
    try {
        closure(zf)
    } finally {
        zf?.close()
    }
}

def dir = new File('Downloads')
def num = 0
dir.eachFileMatch(~/.*\.zip/) { file ->
    file.zipFileWith { zf -> num += zf.size() }
}
println num

Solution 4: Add an eachZipFile(closure) method to the class File:

import java.util.zip.ZipFile

File.metaClass.eachZipFile = { closure ->
    delegate.eachFileMatch(~/.*\.zip/) { file ->
        def zf = new ZipFile(file)
        try {
            closure(zf)
        } finally {
            zf?.close()
        }
    }
}

def dir = new File('Downloads')
def num = 0
dir.eachZipFile { zf -> num += zf.size() }
println num