How to identify whether a file is elf file using C language function？

Question

In my program , I want to identify whether a file is ELF(Executable and Linkable Format) type. How to identify whether a file is elf file using C language function?

Answer 1

If the only thing you want to do is test whether the file is ELF or not, then read the first 16 bytes to check the file identity. The first four bytes will equal {0x7f, 'E', 'L', 'F'}. The remaining bytes can vary, but checking them will help you be even more certain that the file is elf. See the elf(3) man page for more detail.

That man page gives enough info for parsing ELF files in general, but if you want to do more than just check the format, then you should probably use a library. See both the Elf Toolchain and the Binary File Descriptor Library.

Update: Yet another alternative is libmagic(3) which will read the ELF header for you. It is probably overkill if you are only interested in ELF, but libmagic also knows about just about every file format worth knowing about.