(newbie) can compile with gcc but not with g++

[Kamaraju Kusumanchi]

Hi all
  I am a newbie regarding c/c++ programming. From what I read, If I 
write a C program, I can compile with both gcc and g++. I'm not able to 
do the later. Here are the details.

I compiled the clapack package (downloaded from netlib) on intel p4 2.8 
using gcc (3.3.3). I am using debian testing. Consider the following program

#include <stdio.h>

int main()
{
  double a[16] = {11,14,15,16,7,10,13,12,5,6,8,9,1,2,3,4};
  /* Actual matrix is     11   7   5  1
   *                      14  10   6  2
   *                      15  13   8  3
   *                      16  12   9  4
   */
  double b[4] = {1.2,3.2,6.2,2.4};
  int M=4,N=1,lda=4,ldb=4,ipiv[4],info, ret;
  int i,j;

  for(i=0; i<4; i++) {
    for(j=0; j<4; j++) {
      printf("%f ", a[i*4+j]);
    }
    printf("\n");
  }
  for(i=0; i<4; i++) printf("%f\n", b[i]);
  dgesv_(&M, &N, a, &lda, ipiv, b, &ldb, &info);
  for(i=0; i<4; i++) printf("%f\n", b[i]);
  // Correct answer is -0.76, 1.83, -0.51, -0.70
  printf("%d\n",info);
 
  return 0;
}

I am able to run this program with gcc using the following commands.

gcc -c -O2 ludecomp.c
gcc ludecomp.o libtmglib.a liblapack.a libblas.a libF77.a libI77.a -lm -lc
./a.out

But when I use g++, I am getting the following error

mv ludecomp.c ludecomp.cpp
g++ -c ludecomp.cpp
ludecomp.cpp: In function `int main()':
ludecomp.cpp:22: error: `dgesv_' undeclared (first use this function)
ludecomp.cpp:22: error: (Each undeclared identifier is reported only 
once for
   each function it appears in.)

Obviously, I am doing something stupid. Could anyone please tell me what 
I am doing wrong and point the right direction. I searched in google, 
this mailing list archives - but they were of no help.

thanks
raju

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