Thread: Find the maximum value in a column of a text file

Hi everyone.

I am a new member. I have some experience with C++ (not a lot) and I want to switch to C. I have problem with finding the maximum value in a column. This is my code

Code:

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


int main()
{
    FILE *fp;
    fp = fopen ("C:\\rocket1.txt", "r");
    float time, altitude, velocity, acceleration, amax, bmax;
    char *save;
    fgets(save, 95, fp);
    while(!feof(fp))
    {
        sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
        printf("%f\n",velocity);
        free(save);
        fgets(save, 95, fp);
    }
    rewind(fp);
    fgets(save, 95, fp);
    sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
    amax = velocity;
    free(save);
    fgets(save, 95, fp);
    while(!feof(fp))
    {
        sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
        if(amax<velocity)
            amax = velocity;
        free(save1);
        fgets(save, 95, fp);
    }


    printf("%s %f\n", "the m aximum is", amax);
    fclose(fp);
    printf("%s", "Enter something:");
    getchar();
    return(0);
}

The first loop will print out all of numbers in the velocity column. The second while loop is looking for the maximum value in that column. It is supposed to print out the max velocity in the end of the second loop. However, when I build and run the program, it's crashed. I run debugger and received "Segmentation fault" error. When I eliminate the second loop, it run just fine. Can you guy help me to point out the error in this code. Thank you very much. I use Code::Block for text editor.

You did not allocate any memory for save to point to.

Thank Matticus and Laserlight to point out my problems and give me some advice. I am really appreciate that. I change the pointer save to an array and change the method of determine end of file. The program run smoothly now. However, I wonder if I want to use pointer, what should I do? I assumed that allocate memory for the pointer mean assign an address for it to point to(fix me if I am wrong).
Hear is the working code

Code:

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

int main()
{
    FILE *fp;
    fp = fopen ("C:\\rocket1.txt", "r");
    float time, altitude, velocity, acceleration, amax;
    char save[50];
    fgets(save, 95, fp);
    while(fgets(save, sizeof(save), fp) != NULL)
    {
        sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
        printf("%f\n",velocity);
        fgets(save, 95, fp);
    }
    rewind(fp);
    fgets(save, 95, fp);
    sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
    amax = velocity;
    fgets(save, 95, fp);
    while(fgets(save, sizeof(save), fp) != NULL)
    {
        sscanf(save, "%f %f %f %f", &time, &altitude, &velocity, &acceleration);
        if(velocity>amax)
        {
            amax = velocity;
        }
        fgets(save, 95, fp);
    }

    printf("%s %f\n", "the maximum is", amax);
    fclose(fp);
    printf("%s", "Enter something:");
    getchar();
    return(0);
}

And here is the file
1.0000000e+01 2.9265380e+03 5.0821200e+02 4.3231640e+01
2.0000000e+01 1.0170240e+04 9.2798610e+02 4.0723180e+01
3.0000000e+01 2.1486260e+04 1.1832420e+03 1.0328000e+01
4.0000000e+01 3.3835080e+04 1.1882285e+03 -9.3307000e+00
5.0000000e+01 4.5250830e+04 1.0899705e+03 -1.0320900e+01
6.0000000e+01 5.5634490e+04 9.8935650e+02 -9.8019000e+00
7.0000000e+01 6.5037960e+04 8.9134700e+02 -9.8000000e+00
8.0000000e+01 7.3461430e+04 7.9334750e+02 -9.7999000e+00
9.0000000e+01 8.0904910e+04 6.9534750e+02 -9.8001000e+00
1.0000000e+02 8.7368380e+04 5.9734700e+02 -9.8000000e+00
1.1000000e+02 9.2851850e+04 4.9934700e+02 -9.8000000e+00
1.2000000e+02 9.7355320e+04 4.0134750e+02 -9.7999000e+00
1.3000000e+02 1.0087880e+05 3.0334400e+02 -9.8008000e+00
1.4000000e+02 1.0342220e+05 2.0534500e+02 -9.7990000e+00
1.5000000e+02 1.0498570e+05 1.3402000e+02 -4.4660000e+00
1.6000000e+02 1.0610260e+05 2.6304000e+02 3.0270000e+01
1.7000000e+02 1.1024650e+05 6.7618500e+02 5.2359000e+01
1.8000000e+02 1.1962630e+05 1.2929950e+03 7.1003000e+01
1.9000000e+02 1.3610640e+05 2.1234700e+03 9.5092000e+01
2.0000000e+02 1.6209570e+05 3.1700000e+03 1.1421400e+02
2.1000000e+02 1.9950640e+05 3.8340050e+03 1.8587000e+01
2.2000000e+02 2.3877580e+05 3.8779450e+03 -9.7990000e+00
2.3000000e+02 2.7706530e+05 3.7799500e+03 -9.8000000e+00
2.4000000e+02 3.1437480e+05 3.6819500e+03 -9.8000000e+00

Code:

unsigned int get_numbers(char* str, double* const num, const unsigned int siz)
{
    char* end;
    unsigned int i;
    for( i = 0; i < siz; ++i ) {
        str = strtok(i? NULL : str, " \t\n");
        if( !str ) { break; }
        num[i] = strtod(str, &end);
        if( end == str ) { break; }
    }
    return i;
}