C fprintf() function

C library function - fprintf()

The fprintf() function is used for printing information to the screen.

Syntax:

int fprintf(FILE *stream, const char *format, ...)

Parameters:

Format strings specify notation, alignment, significant digits, field width, and other aspects of output formats. It can contain ordinary alphanumeric characters; along with escape characters, conversion specifiers, and other characters, organized as shown below:

Flags

The alignment of the output can be controlled using any of the optional flags listed below:

Field Width and Precision Specifications

By including these options in the format string, you can control the width and precision of the output:

Conversion Characters

The conversion characters specify the output notation:

Escape Characters

The following tables describe the non-alphanumeric characters found in format specification strings:

Return value

• If successful, the total number of characters written is returned otherwise, a negative number is returned.

Example: fprintf() function

Following example create a file test.txt with the uses of fprintf() function.

#include <stdio.h>
int count [12] = {1}; 
int main(void) {
  int i, j;
  i = 100;
  FILE * stream;
  stream = fopen("test.txt", "w");
  fprintf(stream,"** Input text with integers using fprintf(): **");
  fprintf(stream,"\nTo output an integer, use %%d in the format string.");
  int num_of_employees = 203;
  fprintf(stream,"\nNumber of employees: %d ", num_of_employees); 
  fprintf(stream,"\nWe can specify the field width (i.e. how many 'spaces' the item prints in). Default is right-justification.");
  num_of_employees = 50;
  fprintf(stream,"\nNumber of employees: %8d ", num_of_employees); 
  fprintf(stream,"\nTo left justify, use a negative number in the field width:");
  fprintf(stream,"\nNumber of employees: %-8d ", num_of_employees); 
  fprintf(stream,"\nThe minimum number of characters required to print the item will be used if the field width is too small or left unspecified.");
  fprintf(stream, "\nNumber of employees: %2d", num_of_employees);
  fprintf(stream,"\n\n** Input text with Floating-point using fprintf(): **");
  double sale_amt = 345.27;
  fprintf(stream,"\nTo print floating point values in fixed notation, use the %%f modifier:");
  fprintf(stream,"\nYour sale amount is $%f today\n", sale_amt);
  fprintf(stream,"\nUse %e for exponential notation:");
  fprintf(stream,"Sale amount is %e today\n", sale_amt);
  fprintf(stream,"\nFurthermore, you can control the decimal precision, which refers to the number of places after the decimal point:");
  fprintf(stream,"\nThe output will be rounded to the appropriate number of decimal places, if necessary.");
  fprintf(stream,"\nSale amount is $%.2f today\n", sale_amt);
  fprintf(stream,"\nThe width of the field can also be controlled, as with integers:");
  fprintf(stream,"\nSale amount is $%9.2f today\n", sale_amt);
  fprintf(stream,"\n** Printing characters and strings: **");
  fprintf(stream,"\nFor characters, use the formatting specifier %%c. Default field size is 1 character");
  char ch = 'A';
  fprintf(stream,"\n%c%c%c\n", '*', ch, '*');
  fprintf(stream,"\nUse %%s%%s for printing strings. The same rules apply to field widths as they do to integers:");
  fprintf(stream,"\n%s%10s%-10sEND\n", "Red", "Green", "White"); 
 
  fclose(stream);
  FILE * fp;
  int c;
  fp = fopen("test.txt", "r");
  while (1) {
    c = fgetc(fp);
    if (feof(fp)) {
      break;
    }
    printf("%c", c);
  }
  fclose(fp);
  return (0);
}

Output:

Output of the said file data:
** Input text with integers using fprintf(): **
To output an integer, use %d in the format string.
Number of employees: 203
We can specify the field width (i.e. how many 'spaces' the item prints in). Default is right-justification.
Number of employees:       50
To left justify, use a negative number in the field width:
Number of employees: 50
The minimum number of characters required to print the item will be used if the field width is too small or left unspecified.
Number of employees: 50

** Input text with Floating-point using fprintf(): **
To print floating point values in fixed notation, use the %f modifier:
Your sale amount is $345.270000 today

Use 3.204834e-317 for exponential notation:Sale amount is 3.452700e+002 today

Furthermore, you can control the decimal precision, which refers to the number of places after the decimal point:
The output will be rounded to the appropriate number of decimal places, if necessary.
Sale amount is $345.27 today

The width of the field can also be controlled, as with integers:
Sale amount is $   345.27 today

** Printing characters and strings: **
For characters, use the formatting specifier %c. Default field size is 1 character
*A*

Use %s%s for printing strings. The same rules apply to field widths as they do to integers:
Red     GreenWhite     END

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