I found on the internet a fine string concatenating function and tried to rewrite its else scope with use of realloc as it was written with use of calloc. However, I failed. Most of the time I tried to use my version of this function the STM32 microcontroller reached HardFault_Handler. With the original code that uses calloc I had no problem like this.

I tried to find what was wrong using debugger built int STM32CubeIDE but to no avail. I don’t know if I have some memory leak or if I calculate byte sizes or lengths incorrectly. Every help and suggestion is deeply appreciated. Thank You in advance!

    void concatenateStrings(char **string, const char *stringToAdd) {

    // Reset *str
    if ( *string!=NULL && stringToAdd==NULL ) {
        free(*string);
        *string=NULL;
        return;
    }

    // Initial copy
    if (*string==NULL) {
        *string=calloc( strlen(stringToAdd)+1, sizeof(char) );
        memcpy( *string, stringToAdd, strlen(stringToAdd) );
    }
    else { // Append
        //WORKING
        char *tmp=NULL;
        uint16_t stringSize=strlen(*string);
        uint16_t stringToAddSize=strlen(stringToAdd);

        tmp=calloc( stringSize+1, sizeof(char) );
        memcpy( tmp, *string, stringSize );
        *string=calloc( stringSize+stringToAddSize+1, sizeof(char) );
        memcpy( *string, tmp, strlen(tmp) );
        memcpy( *string + stringSize, stringToAdd, stringToAddSize );
        free(tmp);

        //NOT WORKING
/*      char *tmp=NULL;
        uint16_t stringSize=strlen(*string);
        uint16_t stringToAddSize=strlen(stringToAdd);

        tmp=realloc(*string, (stringSize+stringToAddSize+1)*sizeof(char));
        //memset(tmp+stringSize, 0, (stringSize+stringToAddSize+1)*sizeof(char)-stringSize*sizeof(char));
        *string=tmp;
        memcpy(*string + stringSize, stringToAdd, stringToAddSize+1);*/

    }

}