json formatter, C (gcc)

json formatter

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

extern char * str2JsonFormat(char *prevStr, char *key, char *valueStr);

// ===========================================================================================================================
//                                       ========  JSON formatter ==========
// ===========================================================================================================================
// Takes three parameters
//   1) 'prevStr' string. If empty, creates a default new JSON formated string. Otherwise adds a ',' (comma)
//   2) 'key' property parameter
//   3) 'valueStr' string parmeter. Can be a 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 before passing as a string parameter.
// Then wraps it in JSON ["key": "value"] string type format and appends it to the previous string and returns the new string.
// Each ["key": "value"] pair is seperated by a "," (comma)
//
// External Library funtions:
//   strlen, strncat, strcat, malloc
//
// Usage: 
//    exampleOutput = str2JsonFormat(lastString, "name", "data");
//
// Example1 output: (if last string was empty)
//  {"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

// 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);

//  if previous string is empty ceate default string
    if (  strlen(prevStr) == 0)
    {
        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 the JSON formatted string
    return out;
}

int main()
{
    char lastString[100];
    char * exampleOutput;

// strcat(lastString, "\0");
    strcat(lastString, "{\"name1\":\"data\"}\0");
    exampleOutput = str2JsonFormat(lastString, "name2", "data");

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

return 0;
}


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