C language file handling common doubts lying

C language file handling common doubts lying

1. It is difficult to use the fopen() function

 FILE *ptr = fopen("file.txt", "r");
if (ptr == NULL) {
  // File opening failed to handle}

Common difficulties: fopen() function fails to open a file, including the file does not exist, insufficient permissions, or restrictions on system resources. In the if statement, determine whether it is successfully opened based on the returned NULL value.

2. The similarities and similarities between getc() and fgetc() functions

 int ch = getc(ptr);
char ch = fgetc(ptr);

Similarities and differences: getc() function returns int type, while fgetc() function returns char type. When using it, fgetc() is more convenient, and you can directly assign the read content to char variable.

3. Notes on fwrite() function

 fwrite(&buffer, sizeof(buffer), 1, ptr);

Note: The third parameter of the fwrite() function specifies the number of elements written. If the write is an array or structure, the number of elements of the array or structure should be passed, rather than the number of bytes.

4. The combination of fseek() and ftell() function

 fseek(ptr, 5, SEEK_SET); // Skip the first 5 bytes of the file long offset = ftell(ptr); // Get the current file pointer position

Co-use: The fseek() function is used to set the file pointer position, and the ftell() function is used to get the current file pointer position. They are often used together, such as reading data at specific locations in a file.

5. Necessity of file closing

 fclose(ptr);

Necessity: Timely closing files is a crucial step in C language file processing. Failure to close the file in time will lead to loss of file content or leakage of system resources.

Practical case: Read the file and print its contents

 #include <stdio.h>
#include <stdlib.h>

int main() {
  FILE *ptr = fopen("file.txt", "r");
  if (ptr == NULL) {
    perror("Error opening file");
    exit(EXIT_FAILURE);
  }

  char ch;
  while ((ch = fgetc(ptr)) != EOF) {
    putchar(ch);
  }

  fclose(ptr);
  return 0;
}

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