Trouble with header file

Question

I got the following error on compiling a c code I wrote. I understand that the problem is in the header file. Can anyone please tell me which all header files are needed to define these functions.

sign.c: In function ‘main’:
sign.c:78: warning: assignment makes pointer from integer without a cast
/tmp/ccnsSeHy.o: In function `sign_data_evp':
sign.c:(.text+0x68): undefined reference to `check_ssl_rv'
sign.c:(.text+0xd5): undefined reference to `check_ssl_rv'
sign.c:(.text+0x13e): undefined reference to `check_ssl_rv'
/tmp/ccnsSeHy.o: In function `main':
sign.c:(.text+0x1ca): undefined reference to `initialize'
sign.c:(.text+0x1d6): undefined reference to `select_engine'
sign.c:(.text+0x20a): undefined reference to `sign_data'
sign.c:(.text+0x216): undefined reference to `clean_engine'
sign.c:(.text+0x21b): undefined reference to `clean_up'
collect2: ld returned 1 exit status

The header files that I have used so far is:

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <netdb.h>
#include <unistd.h>
#ifdef __VMS
#include <socket.h>
#include <inet.h>

#include <in.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif

#include <openssl/crypto.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

Operating platform: Linux Thanks in advance.

Answer 1

try with this gcc sslprogname.c -o sslprogname -Wl,-Bstatic -lssl -Wl,-Bdynamic -lssl3 -lcrypto.It worked for me

Answer 2

You understand it wrong. It does not complain about unknown function prototype, it complains during the linking. So you probably forgot to link with some library or some object file.