access pointer to double array

Question

I have these structs:

typedef struct {
    char *start;
    char *loops;
    char *tolerance;
    double *numbers;
} configuration;

typedef struct {
    bool help;
    bool debug;
    const char *configFile;
    const char *inputFile;
    const char *outputFile;
    bool parallel;
    int fragmentSize;

} options;

When inputFile is NULL I set the double pointer(config.numbers) to the array: double numbers[] = {3,5,7}; If there is an inputFile I read numbers from it into the array numberList After that I set the pointer config.numbers to numberList. This is the code:

//Safe number list into config
    if(opt.inputFile == NULL) {

        config.numbers = &numbers[0];
        lines = 3;
    } else {
        //Count lines|numbers in file
        FILE* fp;
        fp = fopen(opt.inputFile,"r");
        int bh = 0;
        while(!feof(fp))
        {
            bh = fgetc(fp);
            if(bh == '\n')
            {
                lines++;
            }
        }
        fclose(fp);
        //End counting

        //Read numbers from file
        fp = fopen(opt.inputFile,"r");
        double numberList[lines];
        double number;
        int n;
        for (n = 0; n < lines; n++) {
            fscanf(fp, "%lg", &number);
            numberList[n] = number;
        }
        //End reading numbers from file
        config.numbers = &numberList[0];

    }
    //End safing number list

When I print numberList in else with this for-Loop:

int z;
for(z = 0; z < lines; ++z) {
      printf("%f\n", numberList[z]));
}

Everything works fine, but when I try to print the array using the pointer with this for-Loop:

int z;
for(z = 0; z < lines; ++z) {
    printf("%f\n", *(config.numbers + z));
}

I get as result something like this:

71861994.719069
28587064.020609
91127582.029965
34937973.383320
49643168.000000
0.000000
0.000000
27369248.460685
54686448.003485
93571557.380991
-nan
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000

So how do I access the pointer correctly or did I something else wrong?

EDIT: The input file looks like this:

95181223.701304
27539279.045323
25701472.780528
29898009.416600
72366798.330269
3326112.825110
79857126.893409
38880807.039738
8199298.711586
42132873.992498
34763372.472843
14076941.001265
79042893.824653
17188914.128202
93208812.499982
42846886.181667
80882719.243356
23444107.325489

I expect the same output.

initialising Lines:

int lines = 0;

@CherubimAnand With that it just counts the first number in the array +1 Like: `95181223.701304 95181224.701304 95181225.701304 95181226.701304` — Alesfatalis, Nov 27 '16 at 13:48
Please not that `&number[0]` can simply be `number`. Also [`while (!feof(file))` is always wrong.](http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong). — Iharob Al Asimi, Nov 27 '16 at 13:52
@iharob Yeah I know it is the same was just one of many tries to fix my problem. Thanks for mentioning it — Alesfatalis, Nov 27 '16 at 13:52
More context is required! Show complete functions instead of portions of the code, because the behavior is dependent on whether the array is returned from a function or used in a single scope. — Iharob Al Asimi, Nov 27 '16 at 13:57
And don't attempt crazy random solutions just to solve your problem. Don't solve the problem until you know exactly why what you did solved it. — Iharob Al Asimi, Nov 27 '16 at 13:57
@iharob This is basicly the whole code. Everything is in main. The rest of the code doesn't access or use any of the listed variables. The array is not returned from a function — Alesfatalis, Nov 27 '16 at 13:58

Iharob Al Asimi · Accepted Answer · 2016-11-27T14:14:56.533

2

You have declared the array inside the else branch of your if and then you attempt to print it outside that scope through the pointer. It means that the array has been already destroyed when you attempt to print it.

You need to use dynamic allocation, or try to rewrite the code in a away that allows the array to be declared/defined in the same scope where you are going to print it.

edited Nov 27 '16 at 14:14

answered Nov 27 '16 at 14:00

Iharob Al Asimi

52,653
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1

If I understand you correctly the pointer is basicly pointing to an destroyed array? – Alesfatalis Nov 27 '16 at 14:01
1

@Alesfatalis Yes! That's why it's not a good idea to use *one* pointer to point to different objects. – Iharob Al Asimi Nov 27 '16 at 14:02
I understand. I wasn't aware of that the array is getting destroyed. I would say you got the correct answer – Alesfatalis Nov 27 '16 at 14:05

access pointer to double array

1 Answers1