How to show output on terminal and save to a file at the same time in C?

Question

This the code I have for printing the contents to a file named output.log:

FILE *openFile(void)
{
    FILE *entry;
    entry = fopen("output.log", "a");
    if (entry != NULL)/*verifying whether it opened*/
    {/*printing the --- separator*/
        fprintf(entry, "---\n");/*unable to write to unopened file*/
    }
    return entry;
}

void writeFile(FILE *entry, char *category, double formerX, double 
formerY, double     latestX, double latestY)
{
    /*writing an entry to the given file, as told in the given 
    document*/
    fprintf(entry, "%4s (%7.3f, %7.3f)-(%7.3f, %7.3f) \n", category, 
    formerX, formerY, latestX, latestY);
}

/*closing the file and checking for errors*/
void closeFile(FILE *entry)
{
    if (ferror(entry))
    {
        perror("Error, can't write to the file");
    }
    fclose(entry);
}

I want to now print the same content (saved in output.log) on the terminal screen. How can I add this functionality?

Here is a section of output.log:

MOVE (  0.000,   0.000)-( 18.000,  -0.000) 
DRAW ( 18.000,  -0.000)-( 19.000,  -0.000)
DRAW ( 19.000,  -0.000)-( 20.000,  -0.000)
DRAW ( 20.000,  -0.000)-( 21.000,  -0.000)
DRAW ( 21.000,  -0.000)-( 22.000,  -0.000)
DRAW ( 22.000,  -0.000)-( 23.000,  -0.000)
DRAW ( 23.000,  -0.000)-( 25.000,  -0.000)
MOVE ( 25.000,  -0.000)-(  0.000,  -0.000)
MOVE (  0.000,  -0.000)-( -0.000,   1.000)
MOVE ( -0.000,   1.000)-( 18.000,   1.000)
DRAW ( 18.000,   1.000)-( 19.000,   1.000)

Answer 1

Ways to solve printing to the terminal and saving output to file

• Using printf() , or fprintf(stdin, ""); to stdin, statement after fprintf();
• Using system("cat output.log"); (works in linux) after writing to file.
• Using function which will print the file after writing like

#include <stdio.h>
void printFile(FILE *fp) {
  char line[2048];
  while (fscanf(fp, "%[^\n]s", line) == 1) {
    printf("%s\n", line);
    fgetc(fp); // OR fseek(fp, 1, 1); To throw away the new line in the input
               // buffer
  }
}
int main() {
  FILE *fp;
  fp = fopen("a.txt", "r");
  if (fp == NULL) {
    printf("Error opening the file\n");
    return 1;
  }
  printFile(fp);
  return 0;
}

• Using linux shell
  ./a.out | tee output.log ./a.out | tee output.log and use normal printf() statement inside your C code.