Return to Home page

Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== Write and read a binary file (fwrite and fread) ======
+**Concepts:**\\
+Functions ''fwrite'' and ''fread'' for writing and reading a binary file.
+**Text:**\\
+After the writing of a vector of structures (the elements of the structure are a vector of characters containing the name of a student, a variable of type ''unsigned int'' containing the student identifier and a variable of type ''float'' containing the average value of the scores of the exams attended by the student), the program must:
+  * open in write mode a file with name "''out.bin''", in order to store in the file the vector of structures
+  * written the file in a binary way by using the function ''fwrite''
+  * close the file
+  * reopen the file for reading it
+  * read the file by using the function ''fread'' and fill the vector of structures with the read data
+  * print all the data contained in the vector of structures
+  * close the file
+**Video solution:**\\
+Video with the explanation of the solution:
+<html>
+<iframe width="560" height="315" src="https://www.youtube.com/embed/bnD1xoQDInk" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+</html>
+**Solution:**\\
+<file C binary_file_fwrite_fread.c>
+/* Write and read a binary file (fwrite and fread) */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#define LEN 50
+#define N_STUD 2
+typedef struct stud{
+  char name[LEN+1];
+  unsigned int id;
+  float average;
+}stud_t;
+int main() {
+  FILE *fp;
+  stud_t student[N_STUD];
+  int i;
+  char row[LEN+1];
+  unsigned int n_stud;
+  strcpy(student[0].name, "Steven");
+  student[0].id = 120000;
+  student[0].average = 25.5;
+  strcpy(student[1].name, "Julia");
+  student[1].id = 120001;
+  student[1].average = 28.5;
+  fp = fopen("out.bin", "w"); /* Open the file for writing */
+  if (fp == NULL){
+    printf("Error: file out.bin cannot be opened\n");
+    exit(1);
+  }
+  /* Write the file */
+  /* NOTE 2: a binary file sometimes cannot be readable
+     correctly in a PC that it is not the one which generates it,
+     because, for instance, integer numbers can be coded with a
+     different number of bytes.
+  */
+  /* Write in binary all the data contained in the structure */
+  fwrite(student, sizeof(stud_t), N_STUD, fp);
+  /* DIMENSION OF THE GENERATED FILE
+     The dimension of the generated file will be:
+     n_stud*sizeof(stud_t)
+     in the case of the computer used to test the program:
+*60 = 120 byte
+   */
+  fclose(fp); /* Close the file */
+  fp = fopen("out.bin", "r"); /* Open the file for reading */
+  if (fp == NULL){
+    printf("Error: file out.bin cannot be opened\n");
+    exit(1);
+  }
+  /* Read the file */
+  n_stud = 0;
+  while( fread(&student[n_stud], sizeof(stud_t), 1, fp) == 1 ) {
+    n_stud++;
+  }
+  fclose(fp); /* Close the file */
+  /* Print the read records */
+  for (i=0; i<n_stud; i++) {
+    printf("%s %d %f\n", student[i].name, student[i].id, student[i].average);
+  }
+  return 0;
+}
+</file>

If you found any error, or if you want to partecipate to the editing of this wiki, please contact: admin [at] skenz.it

You can reuse, distribute or modify the content of this page, but you must cite in any document (or webpage) this url: https://www.skenz.it/cs/c_language/write_and_read_a_binary_file?do=diff&rev2%5B0%5D=1551188114&rev2%5B1%5D=1551188114&difftype=sidebyside