Showing an array of Doubles - c

Question

I want to write a function to transform an array of n doubles to an string, a show function, something like:
struct vec { uint64_t n; double *x; };
char *show(struct vec *v) {...}
Notice that I don't want to print them, only do a serialization into a string.
How can I do this in C?

Answer 1

You can do something like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define MAX_DOUBLE_LENGTH 15
typedef struct
{
size_t n;
double* x;
} DoubleArray;
int ShowArray(const DoubleArray* const doubleArrayPtr, char** const resultStringPtr)
{
int errorCode = 0;
char* tempStr = NULL;
char str[MAX_DOUBLE_LENGTH + 2]; /* 1 for trailing space and 1 for null-terminator */
size_t N = 0;
size_t i = 0;
if (doubleArrayPtr == NULL || resultStringPtr == NULL)
{
errorCode = 1;
}
else
{
if (doubleArrayPtr->n != 0)
{
/*
calculating max string length from:
str = <double01> <space> <double02> <space> <double03> <null-terminator>
ex.: str = '3.25 4.75 0.01 5.678\0'
*/
N = doubleArrayPtr->n * MAX_DOUBLE_LENGTH + doubleArrayPtr->n;
tempStr = malloc(N * sizeof(*tempStr));
if (tempStr == NULL)
{
errorCode = 1;
}
else
{
memset(tempStr, 0, N * sizeof(*tempStr));
for(i = 0; i < doubleArrayPtr->n; i++)
{
sprintf(str, "%.6f ", doubleArrayPtr->x[i]);
strcat(tempStr, str);
}
tempStr[strlen(tempStr) - 1] = '\0';
/* string formed -- allocating buffer for result */
(*resultStringPtr) = malloc((strlen(tempStr) + 1) * sizeof(**resultStringPtr));
if ((*resultStringPtr) == NULL)
{
errorCode = 1;
}
else
{
/* exporting result */
memcpy((*resultStringPtr), tempStr, strlen(tempStr) * sizeof(*tempStr));
(*resultStringPtr)[strlen(tempStr)] = '\0';
}
}
free(tempStr);
tempStr = NULL;
}
}
return errorCode;
}
int main(void)
{
/* test code part */
DoubleArray d;
char* s = NULL;
size_t i = 0;
srand(time(NULL));
d.n = rand() % 21;
d.x = malloc(d.n * sizeof(*d.x));
for(i = 0; i < d.n; i++)
{
d.x[i] = (rand() % 99999) / 100.0;
printf("[%d] = %f\n", i, d.x[i]);
}
ShowArray(&d, &s);
printf("str = '%s'\n", s);
free(d.x);
free(s);
return 0;
}