Can not find function that defined in header file in C (JNI)

Question

I made .c file to use in JNI. .java, .h, .c and compiled nicely:D My environment is Windows 7 64 bits.

However, the problem that I am facing is about another external library. I received a library that consists of one header file and one lib file. What I did is below.

I. copy XXX.h and XXX.lib into the same physical directory where original JNI files are. in my case: C:\Users\JY\worspace\Test\org\owls\src\jni\ and now I have these files in there:

• Original files:

  • IIS.java

  • IIS.class

  • org_owls_jni_IIS.h

  • IIS.c

• Newly added:

  • XXX.h

  • XXX.lib

II. added the directive #include "XXX.h" to the .c file. So IIS.c now looks like this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "org_owls_jni_IIS.h"
#include "XXX.h"

JNIEXPORT jint JNICALL Java_org_owls_jni_IIS_doIIS
    (JNIEnv* env, jobject jobj, jstring jtarget, jstring jdest, jstring jimage){

    jboolean iscp;
    int video_len = 0;
    char* a = "aaa";
    const char* ctarget = (*env)->GetStringUTFChars(env, jtarget, &iscp);
    const char* cdest = (*env)->GetStringUTFChars(env, jdest, &iscp);
    const char* cimage = (*env)->GetStringUTFChars(env, jimage, &iscp);

    fprintf(stderr, "VIDEO [ %s ] THUMBNAIL [ %s ]\n", ctarget, cdest);
    sprintf(tmp, "C : %s\t%s", ctarget, cdest);
    fprintf(stderr, "%s\n", tmp);

    Call_XXX(a);

    (*env)->ReleaseStringUTFChars(env, jtarget, ctarget);
    (*env)->ReleaseStringUTFChars(env, jdest, cdest);
    (*env)->ReleaseStringUTFChars(env, jimage, cimage);
    return (jint)video_len;

}

Call_XXX() is defined in XXX.h and it receives an argument type of char *.

III. compiling with the cl command via VS2012 x64 Native Tools Command Prompt. Command line is:

cl IIS.c -Feiis.dll -LD -MD
cl IIS.c -Feiis.dll -LD -MD -link XXX.lib

IV. Now the problem comes. Normally, If adding a header file succeeds, there's no problem with calling a function which is declared in that header. But in my case, there's an error. Symptoms are below.

• just adding the header file does not result in a compiler error (the compilation succeededs.)

• Using the function that is declared in the header file results in a linker error (LNK2019).

error messages are :

IIS.c
Microsoft (R) Incremental Linker Version 11.00.50727.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:iis.dll 
/dll 
/implib:iis.lib 
IIS.obj 
   iis.lib 라이브러리 및 iis.exp 개체를 생성하고 있습니다.
IIS.obj : error LNK2019:Call_XXX 외부 기호(참조 위치: Java_org_owls_jni_IIS_doIIS 함수)에서 확인하지 못했습니다.
iis.dll : fatal error LNK1120: 

I erased some messages, because those are not in English. But since I left the error codes, I guess that there is no problem with recognizing causes and the situation.

Answer 1

You need to tell the linker that in can look into XXX.lib for any functions it needs to link. It doesn't do that just because the file is in your project directory.

One way to do that is in some source file that is complied, say in IIS.c, after #include "XXX.h"

#pragma comment(lib, "XXX.lib")

See this MS Knowledge Base article.