Use reference argument to pass string to loop function

src/cluster/cluster.cpp

@@ -733,7 +733,7 @@ void cluster(const string& config_file, const string& data_file, const string& o
 }
 
 
-int cluster_jxi488_cycle(int jxi488, ScattererConfiguration *sconf, GeometryConfiguration *gconf, ScatteringAngles *sa, C1 *c1, C1_AddOns *c1ao, C2 *c2, C3 *c3, C4 *c4, C6 *c6, C9 *c9, FILE *output, string output_path, double *gaps, double **tqse, dcomplex **tqspe, double **tqss, dcomplex **tqsps, double ****zpv, double **gapm, dcomplex **gappm, double *argi, double *args, double **gap, dcomplex **gapp, double **tqce, dcomplex **tqcpe, double **tqcs, dcomplex **tqcps, double *duk, fstream &tppoan, double **cextlr, double **cext, double **cmullr, double **cmul, double *gapv, double *tqev, double *tqsv, double *u, double *us, double *un, double *uns, double *up, double *ups, double *unmp, double *unsmp, double *upmp, double *upsmp, double &scan, double &cfmp, double &sfmp, double &cfsp, double &sfsp, double sqsfi, dcomplex arg, double wn, double vk, Logger *logger)
+int cluster_jxi488_cycle(int jxi488, ScattererConfiguration *sconf, GeometryConfiguration *gconf, ScatteringAngles *sa, C1 *c1, C1_AddOns *c1ao, C2 *c2, C3 *c3, C4 *c4, C6 *c6, C9 *c9, FILE *output, const string& output_path, double *gaps, double **tqse, dcomplex **tqspe, double **tqss, dcomplex **tqsps, double ****zpv, double **gapm, dcomplex **gappm, double *argi, double *args, double **gap, dcomplex **gapp, double **tqce, dcomplex **tqcpe, double **tqcs, dcomplex **tqcps, double *duk, fstream &tppoan, double **cextlr, double **cext, double **cmullr, double **cmul, double *gapv, double *tqev, double *tqsv, double *u, double *us, double *un, double *uns, double *up, double *ups, double *unmp, double *unsmp, double *upmp, double *upsmp, double &scan, double &cfmp, double &sfmp, double &cfsp, double &sfsp, double sqsfi, dcomplex arg, double wn, double vk, Logger *logger)
 {
   int nxi = sconf->number_of_scales;
   logger->log("INFO: running scale iteration " + to_string(jxi488) + " of " + to_string(nxi) + ".\n");