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POconverting a string to double using atof in c
 

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  1. POconverting a string to double using atof in c
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    <p>I am trying to read from a file and store it in a matrix using c. The code I have is </p> <pre><code>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 a line buf[0] = 0; fgets(buf, BUFSIZ, fp); // if it's a blank line, ignore if(strlen(buf) &gt; 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 } </code></pre> <p>The code works well when I take p1 and convert it to integer using atoi. But when I use atof to convert the value to float, I am getting a zero. my input looks like</p> <pre><code>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 </code></pre> <p>After I read this input, when I print it I am getting</p> <pre><code> 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 </code></pre> <p>when I use atoi , I get the following </p> <pre><code>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 </code></pre> <p>Can someone please help me?</p>
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    1. COHi, Lopez - SUGGESTIONS: 1) input the line with `fgets()`, just like you're doing now. 2) Explicitly check for errors/null data in your `fopen()` and your `fgets()`. 3) Substitute `sscanf()` in place of atoi() and atof(). Do this so you can check for formatting errors. 4) You can forget about the `strtok()` stuff: sscanf() lets you parse all the variables in the string at once. 5) Let us know how it works for you :)!
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    2. COPerfect. Thank you very much !
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