函数执行后结构数组中的值丢失

Question

I am working on ac code that holds a structure that hosts some values which I call range.

My purpose is to use this so called range dynamically (holding different amount of data at every execution). I am now provisionally using the # define comp instead. This so called range gets updated every time I call my update_range though the use of s1 structure (and memory allocations).

What I found weird is that when I introduced a "show_range" function to output the actual values inside/outside the update function I realized that I loose the first two values. Here is the code. Any suggestions on that? Thanks in advance!

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <errno.h>
#include <string.h>
#include <complex.h>
#define comp 1024

// struct holding a complex-valued range
struct range {
    int dimensions;         /* number of dimensions */
    int* size;              /* array holding number of points per dimension */
    complex double* values; /* array holding complex valued */
    int components; /* number of components that will change on any execution*/
};

// parameters to use in function
struct s1 {
    int tag;
    struct range* range;
};

int update_range(struct s1* arg);
int show_range(struct range* argrange, char* message);
int copy_range(struct range* in, struct range* out);

int main(void) {
    int ret = 0;
    struct s1 s1;
    s1.tag = 0;
    s1.range = malloc(sizeof(struct range));
    update_range(&s1);
    show_range(s1.range, "s1.range inside main function");

    return ret;
}

////////////////////////////////////////////
int update_range(struct s1* arg) {
    int ret = 0;
    int i;
    struct range range;
    range.dimensions = 1;
    range.size = malloc(range.dimensions * sizeof(int));
    range.components = comp;
    range.size[0] = range.components; // unidimensional case
    range.values = malloc(range.components * sizeof(complex double));
    for (i = 0; i < range.components; i++) {
        range.values[i] = (i + 1) + I * (i + 1);
    }
    show_range(&range, "range inside update_range function");

    arg->range->size =
        malloc(range.dimensions * sizeof(int)); // size was unknown before
    arg->range->values =
        malloc(comp * sizeof(complex double)); // amount of values was unknown
    copy_range(&range, arg->range);
    show_range(arg->range, "arg->range inside update_range function");

    if (range.size)
        free(range.size);
    range.size = NULL;
    if (range.values)
        free(range.values);
    range.values = NULL;
    return ret;
}

////////////////////////////////////////////
// Show parameters (10 first values)
int show_range(struct range* argrange, char* message) {
    int ret = 0;
    vint i;
    printf("   ******************************\n");
    printf("   range in %s \n", message);
    printf("   arg.dimensions=%d \n", argrange->dimensions);
    printf("   arg.size[0]=%d \n", argrange->size[0]);
    printf("   argrange.components=%d \n", argrange->components);
    printf("      first 10 {Re} values: \n");
    for (i = 0; i < 10; i++) {
        printf("   argrange.values[%d]=%f\n", i, creal(argrange->values[i]));
    }
    printf("\n");
    return ret;
}

////////////////////////////////////////////
// copy range
int copy_range(struct range* in, struct range* out) {
    int ret = 0;

    if (in == NULL) {
        fprintf(stderr, "error: in points to NULL (%s:%d)\n", __FILE__,
                __LINE__);
        ret = -1;
        goto cleanup;
    }
    if (out == NULL) {
        fprintf(stderr, "error: out points to NULL (%s:%d)\n", __FILE__,
                __LINE__);
        ret = -1;
        goto cleanup;
    }

    out->dimensions = in->dimensions;
    out->size = in->size;
    out->values = in->values;
    out->components = in->components;

cleanup:
    return ret;
}

Answer 1

Your copy_range function is broken, because it copy only pointer to size and values and not the memory. After you call free(range.size); and free(range.values); you are deleting mamory also from original object but without setting its pointers back to NULL.

After calling update_range, s1.range has non NULL pointers in size and values, but they are pointing to deleted memory.

Answer 2

You are experiencing undefined behaviour (UB) due to accessing freed memory. Your copy_range() function only does a shallow copy of the two pointer fields so when you run free(range->size) you make arg->range->size invalid.

You should make copy_range() a deep copy by allocating and copying the pointer contents like:

out->size = malloc(in->dimensions * sizeof(int));
memcpy(out->size, in->size, in->dimensions * sizeof(int));

out->values = malloc(in->components * sizeof(complex double));
memcpy(out->values , in->values, in->components * sizeof(complex double));

Answer 3

There are not 10 items to print, so the lines:

printf("      first 10 {Re} values: \n");
for (i = 0; i < 10; i++) {
    printf("   argrange.values[%d]=%f\n", i, creal(argrange->values[i]));
}

Will be printing from random memory.
a much better method would be:

    printf("      first %d {Re} values: \n", min(argrange.components,10));
for (i = 0; i < argrange.components; i++) {
    printf("   argrange.values[%d]=%f\n", i, creal(argrange->values[i]));
}

The above is just one of many problems with the code.  
I would suggest executing the code using a debugger to get the full story.  
as it is, the code has some massive memory leaks due mostly 
to overlaying malloc'd memory pointers.  
for instance as in the following:

arg->range->size =
    malloc(range.dimensions * sizeof(int)); // size was unknown before
arg->range->values =
    malloc(comp * sizeof(complex double)); // amount of values was unknown