How do I search the content of 7-Zip archives (.7z)?

On Windows, use a command prompt:

cd C:\Program Files\7-Zip
7z

To search for a specific file, e.g. namefile:

7z l compressed.tar namefile -r

Video tutorial: Search files with 7-Zip

WinRAR can do it. However, let's face that fact it involves unpacking it, even though WinRAR does it seamlessly.

As others have said, no there is no way. To examine the contents of a file, it needs to be unpacked (regardless of if the files are compressed solid or not or if they are encrypted or not). The only way that you can avoid having to decompress the files is if they are added with the store method (ie, not compressed at all, just globbed together).