file io - converting a string to double using atof in c -


i trying read file , store in matrix using c. code have 

readsparseinput (int nvtxs,int nsize, double  vector[], int rowptr[] ,int colind [] , double values[]) {     int index,row=0,column=0;     int sparsity_value, nvtxs_local;     int vector_size =50;     double value;     double  randvect[vector_size];     int  length=0;     char buf[bufsiz];     file *fp;     fp=fopen("/home/lopez380/parallel/m10-a.ij", "r");     index =0;     nvtxs_local = 0;     rowptr[0] = 0;     char *p1;     while ( !feof(fp))     {          // null buffer, read line         buf[0] = 0;         fgets(buf, bufsiz, fp);         // if it's blank line, ignore         if(strlen(buf) > 1)          {             p1 = strtok(buf, " ");             row=atoi(p1);             #ifdef debug                 fprintf(stdout, "row : %d ", row);             #endif             p1 = strtok(null, " ");             column=atoi(p1);             #ifdef debug                 fprintf(stdout, "column : %d ", column);             #endif             p1 = strtok(null, " ");             value=atof(p1);             #ifdef debug                 fprintf(stdout, "value : %g\n ", value);             #endif         }      }     fclose(fp);      #ifdef debug     printf("lfilelen = %d\n", length);     #endif  }

the code works when take p1 , convert integer using atoi. when use atof convert value float, getting zero. input looks like

0 0 1.76420546156578 0 3 -4.80876443295632 0 6 1.20260376970926 0 9 3.30693451100554 1 1 1.13901264701619 1 4 0.370358438592131 1 7 -0.551593262343761

after read input, when print getting

 row : 0 column : 0 value : 0  row : 0 column : 3 value : 0  row : 0 column : 6 value : 0  row : 0 column : 9 value : 0  row : 1 column : 1 value : 0  row : 1 column : 4 value : 0  row : 1 column : 7 value : 0

when use atoi , following 

row : 0 column : 0 value : 1  row : 0 column : 3 value : -4  row : 0 column : 6 value : 1  row : 0 column : 9 value : 3  row : 1 column : 1 value : 1  row : 1 column : 4 value : 0  row : 1 column : 7 value : 0

can please me?

i discourage using atoi() , atof(), unless implementation provides error checking (e.g. atoi() , atof()" update errno.

i prefer fscanf(): illegal input can detected return value.

example:

if (fscanf(fp, "%f", &f) == 1)     ...all ok... else     ...eof or conversion failure...

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