json string formatter, C (gcc)

Language: Layout:

#include <stdio.h>     // printf
#include <string.h>    // strlen, strcat, strncat, memmove
#include <stdlib.h>    // malloc
#include <ctype.h>     // isspace

extern void removeWhiteSpace(char *str);
extern char * str2JsonFormat(char *prevStr, char *key, char *valueStr);

/*
 =============================================================================================
                     ========  Remove whitespace from string ==========
 =============================================================================================
   reference: https://www.geeksforgeeks.org/remove-spaces-from-a-given-string/

This will remove all white space characters (space, tab, CR, LF) from string. It modifies
the string.

1) Initialize 'count' = 0 (Count of non-space character seen so far)
    2) Iterate through all characters of given string, do following
         a) If current character is non-whitepace, then put this character
            at index 'count' and increment 'count'
    3) Finally, write a NULL ('\0') at index 'count'

Enhancement
   1) make a copy the initial string to a temp variable using memmove
   2) now remove whitespace from temp variable
   3) return the temp variable

External Library functions:
     isspace

Usage: (string contains tabs, spaces and newlines)
       remove_spaces("  {     "key1"     		       :	    "data1"  	 }  ");

Example output:
    {"key1":"data1"}
*/
void removeWhiteSpace(char *str)
{
    int count = 0;            // Count of non-space characters
    int i     = 0;            // iterate over each character in string

// iterate over each character in string.
    for (i = 0; str[i]; i++)
    {
        // If current character is NOT a whitespace, then move it to index 'count++'
        if ( !isspace(str[i]) ) { str[count++] = str[i]; }
    }

str[count] = '\0';        // add a null at the new end of string;
}

/*
 =============================================================================================
                           ========  JSON formatter ==========
 =============================================================================================
   Takes three parameters
     1) 'prevStr' string. If empty string, or an empty object creates a default new JSON formated
         string. Otherwise adds a ',' (comma)
     2) 'key' property parameter
     3) 'valueStr' string parameter. Can be any character, string, integer or float viewed as a
         string type.

NOTE: This will NOT convert integers and floats to strings. It does not know how many
           decimal places to convert. This will need to be done as a separate step before passing
           it as a string parameter to this function.

After checking validity of previous string and removing whitespace, it then wraps it in
   JSON ["key": "value"] string type format, appends it to the previous string and returns the
   new string. Each ["key": "value"] pair is separated by a "," (comma)

External Library functions:
     strlen, strncat, strcat, malloc

Usage:
      exampleOutput = str2JsonFormat(lastString, "name", "data");

Example1 output: (if lastString="" or lastString={} )
    {"name":"data"}

Example2 output: (if last string was NOT empty)
    {"name":"data","name":"data"}

*/
char * str2JsonFormat(char *prevStr, char *key, char *valueStr)
{
    char *out;           // formatted JSON return string
    int outSize  = 0;    // size of formatted JSON return string
    int overhead = 8;    // extra characters for JSON formatting
    // char d[100] = {};
    // int i, j;

// need to calculate space needed for formatted return string
    //    Add length of previous string input parameter
    //    Add length key string input parameter
    //    Add length valueStr string input parameter
    //    Add overhead characters to reflect JSON formatting
    outSize = strlen(prevStr) + strlen(key) + strlen(valueStr) + overhead;
    // need to malloc memory location
    out = (char *) malloc(sizeof(char) * outSize);

// remove all white space characters (space, tab, CR, LF)
   removeWhiteSpace(prevStr);

//  if previous string is empty or empty object create default string
    if (  (strlen(prevStr) == 0) |
          ( (prevStr[0] == '{') & (prevStr[1] == '}') )   )
    {
        strcat(out, "{");                            // add a "{" (left brace)
    }
    // otherwise append previous string to formatted return string with slight modifications
    else
    {
        strncat(out, prevStr, strlen(prevStr)-1 );   // delete the last '}' (right brace)
        strcat(out, ",");                            // and add ',' (comma)
    }

// concatenate new key / value pair with JSON formatting
    strcat(out, "\"");       // add a '"' (double quote)
    strcat(out, key);
    strcat(out, "\":\"");    // complete the (double quote), add ':' (colon), start a new (double quote)
    strcat(out, valueStr);
    strcat(out, "\"}");      // add a '}' (right brace)

// return pointer to the new JSON formatted string
    return out;
}

int main()
{
    char *lastString;
    char *jsonTemp;

lastString = (char *) malloc(sizeof(char) * strlen("") );
    // memmove(lastString, "        { \"key1\"      : \"data1\"   }       \0", strlen("        { \"key1\"      : \"data1\"   }       \0") );
    // strcat(lastString, "\0");
    // strcat(lastString, "        { \"key1\"      : \"data1\"   }       \0");

jsonTemp   = str2JsonFormat(lastString, "key2", "data2");
    lastString = (char *) malloc(sizeof(char) * strlen(jsonTemp) );
    memmove(lastString, jsonTemp, strlen(jsonTemp) );

jsonTemp   = str2JsonFormat(lastString, "key3", "data3");
    lastString = (char *) malloc(sizeof(char) * strlen(jsonTemp) );
    memmove(lastString, jsonTemp, strlen(jsonTemp) );

jsonTemp   = str2JsonFormat(lastString, "key4", "data4");
    lastString = (char *) malloc(sizeof(char) * strlen(jsonTemp) );
    memmove(lastString, jsonTemp, strlen(jsonTemp) );

printf(" output length is %li \r\n", strlen(lastString) );
    printf(" output is %s \r\n", lastString);

return 0;
}

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Compilation time: 0.23 sec, absolute running time: 0.18 sec, cpu time: 0.01 sec, memory peak: 5 Mb, absolute service time: 0,55 sec