Math.h not found even though `-lm` is set

What causes could there be, that gcc does not link to math.h even though I set the flag -lm?

me@mycomputer开发者_StackOverflow中文版$ g++ template_gold.cpp -o template_gold -lm
template_gold.cpp: In function ‘void computeGold(valpoint*, centroid*, int)’:
template_gold.cpp:68: error: ‘max’ was not declared in this scope
template_gold.cpp:70: error: ‘abs’ was not declared in this scope

I am sorry, if this is a dupe, but searching the googles and SO I found only post suggesting to set the -lm.

Offending Code

#include <math.h>
#include "kmeans.h"
extern "C" 
void computeGold( valpoint* h_idata, centroid* h_centroids, int numClusters);
...
for (long valindex = 0; valindex<1024*1024; valindex++)
    {
        minDistance = 0xFFFFFFFF;
        for (k = 0; k<numClusters; k++)
            if (max((long)(h_idata[valindex].value - h_centroids[k].value))<minDistance)
            {
                minDistance = abs((long)(h_idata[valindex].value - h_centroids[k].value));
                myCentroid = k;
            }

        h_idata[valindex].centroid = h_centroids[myCentroid].value;

    }
}

You probably forgot to use std::max, or you forgot adding using namespace std. Try

void void computeGold(valpoint* ..., centroid* ..., int ...)
{
    using namespace std; /* or using std::max etc. */
}