[Dev-C++] Is a struct preserved when used into a cpp file?

Hello,

a) I have a .h (header file) that declares a struct:
...
typedef struct {
   UINT4 state[4];  /* state (ABCD) */
   UINT4 count[2];  /* number of bits, modulo 2^64 (lsb first) */
   unsigned char buffer[64];  /* input buffer */
} MD5_CTX;
...

b) and I have .c (C source file) that uses the header above:
...
void MD5Init(MD5_CTX *context);
...

c) I have created a .lib (library file) with the functions above.

I have used the header file above into a .cpp (C++ source file). The .cpp
file uses the .lib functions, but the compiles says "Unresolved external
MD5Init(MD5_CTX*) ...".

I think the .lib was included correctly on the project, so is a struct
preserved when used into a cpp file?

Thanks in advance, Vinicius.

PS: I'm using actually the Borland C++Builder 3 IDE for this project, but my
doubts is concerned about the theory, excuse me for anything.