Why does the code generate garbage at the beginning of the vector?

Question

Why does the code generate garbage at the beginning of the vector?

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#1 by (2 votes)

0

The following code generates an unexpected result, at the end of the loop the first positions of the vector are with garbage stored, does anyone know why this is happening, and where is the error?

OBS. The code has the same behavior in both C and C ++ (gcc and g ++ compilers)

Code:

    #include<stdio.h>
    #include<stdlib.h>


    int V = 10;
    int E = 20;

    int main() {
        double sol[3*E + V];
        int ind[3*E + V];
        double val[3*E + V];
        double ub[3*E + V];
        double obj[3*E + V];
        char **varname;
        char vtype[V];
        int erro;


        varname = (char**) malloc((3*E+V)*sizeof(char**));

        for (int i = 0; i < V; ++i) {
            obj[i] = 0;
            vtype[i] = 'B';
            ub[i] = 1;
            varname[i] = (char*) malloc(sizeof(char*)*10);
            sprintf(varname[i], "y_%i", i);
        }

        int k = 0;
        for (int i=V; i < (V+3*E); i+=3) {
            for(int j=0; j < 3; ++j) {
                obj[i+j] = 0;
                vtype[i+j] = 'B';
                ub[i+j] = 1;
                varname[i+j] = (char*) malloc(sizeof(char*)*15);
                sprintf(varname[i+j], "x_%i_%i_%i", 0, 0, j);
            }
            k++;
        }

        for (int i=0; i < (V+3*E); ++i) {
            printf(" obj[%d]: %.1f \t(%s), \t (%c) <= (%.1f)\n", i, obj[i], varname[i], vtype[i], ub[i]);
        }

        getchar();

    }

Output:

    Success time: 0 memory: 2296 signal:0
     obj[0]: 156842099844.5     (y_0),   (B) <= (1.0)
     obj[1]: 156842099844.5     (y_1),   (B) <= (1.0)
     obj[2]: 156842099844.5     (y_2),   (B) <= (1.0)
     obj[3]: 156842099844.5     (y_3),   (B) <= (1.0)
     obj[4]: 156842099844.5     (y_4),   (B) <= (1.0)
     obj[5]: 156842099844.5     (y_5),   (B) <= (1.0)
     obj[6]: 0.0    (y_6),   (B) <= (1.0)
     obj[7]: 0.0    (y_7),   (B) <= (1.0)
     obj[8]: 0.0    (y_8),   (B) <= (1.0)
     obj[9]: 0.0    (y_9),   (B) <= (1.0)
     obj[10]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[11]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[12]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[13]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[14]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[15]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[16]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[17]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[18]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[19]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[20]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[21]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[22]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[23]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[24]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[25]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[26]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[27]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[28]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[29]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[30]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[31]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[32]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[33]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[34]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[35]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[36]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[37]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[38]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[39]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[40]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[41]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[42]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[43]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[44]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[45]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[46]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[47]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[48]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[49]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[50]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[51]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[52]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[53]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[54]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[55]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[56]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[57]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[58]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[59]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[60]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[61]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[62]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[63]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[64]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[65]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[66]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[67]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[68]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[69]: 0.0   (x_0_0_2),   (B) <= (1.0)

Hugs!

c gcc

asked by anonymous 29.09.2016 / 18:13

1 answer

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score 2 · Answer 1

Your vtype array has only size 10, but you write in it as if it were the same size as the others. The way local variables are structured, you end up writing over the memory of the other arrays. In this case you are writing over the obj array, which ends up generating the garbage you have noticed.