Remove spaces from a string in C

Here is the simplest thing i could think of. Note that this program uses second command line argument (argv[1]) as a line to delete whitespaces from.

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

/*The function itself with debug printing to help you trace through it.*/

char* trim(const char* str)
{
    char* res = malloc(sizeof(str) + 1);
    char* copy = malloc(sizeof(str) + 1);
    copy = strncpy(copy, str, strlen(str) + 1);
    int index = 0;

    for (int i = 0; i < strlen(copy) + 1; i++) {
        if (copy[i] != ' ')
        {
            res[index] = copy[i];
            index++;
        }
        printf("End of iteration %d\n", i);
        printf("Here is the initial line: %s\n", copy);
        printf("Here is the resulting line: %s\n", res);
        printf("\n");
    }
    return res;
}

int main(int argc, char* argv[])
{
    //trim function test

    const char* line = argv[1];
    printf("Here is the line: %s\n", line);

    char* res = malloc(sizeof(line) + 1);
    res = trim(line);

    printf("\nAnd here is the formatted line: %s\n", res);

    return 0;
}

/* Function to remove all spaces from a given string.
   https://www.geeksforgeeks.org/remove-spaces-from-a-given-string/
*/
void remove_spaces(char *str)
{
    int count = 0;
    for (int i = 0; str[i]; i++)
        if (str[i] != ' ')
            str[count++] = str[i];
    str[count] = '\0';
}

This is implemented in micro controller and it works, it should avoid all problems and it is not a smart way of doing it, but it will work :)

void REMOVE_SYMBOL(char* string, uint8_t symbol)
{
  uint32_t size = LENGHT(string); // simple string length function, made my own, since original does not work with string of size 1
  uint32_t i = 0;
  uint32_t k = 0;
  uint32_t loop_protection = size*size; // never goes into loop that is unbrakable
  while(i<size)
  {
    if(string[i]==symbol)
    {
      k = i;
      while(k<size)
      {
        string[k]=string[k+1];
        k++;
      }
    }
    if(string[i]!=symbol)
    {
      i++;
    }
    loop_protection--;
    if(loop_protection==0)
    {
      i = size;
      break;
    }
  }
}

While this is not as concise as the other answers, it is very straightforward to understand for someone new to C, adapted from the Calculix source code.

char* remove_spaces(char * buff, int len)
{
    int i=-1,k=0;
    while(1){
        i++;
        if((buff[i]=='\0')||(buff[i]=='\n')||(buff[i]=='\r')||(i==len)) break;
        if((buff[i]==' ')||(buff[i]=='\t')) continue;
        buff[k]=buff[i];
        k++;
    }
    buff[k]='\0';
    return buff;
}