Writing to a file with stdio - c

Question

I am using an example code from the wiringPi library to read data from Arduino to Raspberry Pi through serial, it is displaying the data correctly with printf("%c", newChar); but I can't write the same data to a text file.
This is the whole file:
/*
Pi_Serial_test.cpp - SerialProtocol library - demo
Copyright (c) 2014 NicoHood. All right reserved.
Program to test serial communication
Compile with:
sudo gcc -o Pi_Serial_Test.o Pi_Serial_Test.cpp -lwiringPi -DRaspberryPi -pedantic -Wall
sudo ./Pi_Serial_Test.o
*/
// just that the Arduino IDE doesnt compile these files.
#ifdef RaspberryPi
//include system librarys
#include <stdio.h> //for printf
#include <stdint.h> //uint8_t definitions
#include <stdlib.h> //for exit(int);
#include <string.h> //for errno
#include <errno.h> //error output
//wiring Pi
#include <wiringPi.h>
#include <wiringSerial.h>
char device[]= "/dev/ttyAMA0";
// filedescriptor
int fd;
unsigned long baud = 9600;
unsigned long timeTemp=0;
unsigned long timeHum=0;
//unsigned long timeLight=0;
//unsigned long timeMotion=0;
//prototypes
int main(void);
void loop(void);
void setup(void);
void setup(){
printf("%s \n", "Raspberry Startup!");
fflush(stdout);
//get filedescriptor
if ((fd = serialOpen (device, baud)) < 0){
fprintf (stderr, "Unable to open serial device: %s\n", strerror (errno)) ;
exit(1); //error
}
//setup GPIO in wiringPi mode
if (wiringPiSetup () == -1){
fprintf (stdout, "Unable to start wiringPi: %s\n", strerror (errno)) ;
exit(1); //error
}
}
void loop() {
// Temperature every 3 seconds
if(millis()-timeTemp>=3000){
serialPuts (fd, "05\n");
// you can also write data from 0-255
// 65 is in ASCII 'A'
//serialPutchar (fd, 5);
timeTemp=millis();
}
// read signal
if(serialDataAvail (fd)){
char newChar = serialGetchar (fd);
FILE * writeTemp = fopen("temp.txt", "w");
printf("%c", newChar);
fputc(newChar, writeTemp);
fflush(stdout);
fclose(writeTemp);
}
// Humidity every 4 seconds
if(millis()-timeHum>=4000){
serialPuts (fd, "06\n");
// you can also write data from 0-255
// 65 is in ASCII 'A'
//serialPutchar (fd, 5);
timeHum=millis();
}
// read signal
if(serialDataAvail (fd)){
char newChar = serialGetchar (fd);
//printf("received from ardiono \n");
printf("%c", newChar);
fflush(stdout);
}
}
// main function for normal c++ programs on Raspberry
int main(){
setup();
while(1) loop();
return 0;
}
#endif //#ifdef RaspberryPi
I've tried different commands, but I'm constantly getting errors for invalid conversions from const char* to char or to FILE.
I just need to write the data from printf("%c", newChar); in a file.

Answer 1

In the line fputc(&newChar, writeTemp);, you're taking a pointer to your character, converting it to int, then writing that to your file. You should just write your character; something like fputc(newChar, writeTemp);. Or fprintf(writeTemp, "%c", newchar); if you prefer printf.

Answer 2

fputc takes a int, not an address. The problem that you are having is because you are passing the address of newChar. change the code to
fputc(newValue, tempFile);
and you should be good to go.
Good luck :)

Answer 3

If you want a printf-like function, use fprintf.
To write your output to a file, you would write
fprintf(writeTemp, "%c", newChar);
Also, the line
char value = printf("%c", newChar);
does not make sense, since value is declared as a char but is assigned the return status from printf.
As another reply points out, the arguments to fputc() are also wrong. You can write
fputc(newChar, writeTemp);

Answer 4

Using append instead of write somehow fixed the problem:
FILE * writeTemp = fopen("temp.txt", "a");
I also had to remove the second request:
/*
// Humidity every 3 seconds
if(millis()-timeHum>=3000){
serialPuts (fd, "06\n");
timeHum=millis();
}
// read signal
if(serialDataAvail (fd)){
char humChar = serialGetchar (fd);
printf("%c", humChar);
fflush(stdout);
}
*/
because it was interfering with the data for some reason, even with different char variable.
Thank you for the answers.