为什么更新模式写入二进制文件不用setvbuf设置缓存
一般在打开文件后，要进行缓存操作，但是下面更新没有用，是否说明更新不需要设置缓存，能否详细帮忙从原理上解答一下#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define MAXLEN 50 // Size of name buffer
void listfile(const char *filename); // List the file contents
int main(void)
{
const char *filename = "mypeople.bin";
char name[MAXLEN]; // Stores a name
size_t length = 0; // Length of a name
int age = 0; // Person's age
char answer = 'y';
FILE *pfile = NULL;
if(fopen_s(&pfile, filename, "wb+"))
{
printf_s("Failed to create file %s.\n", filename);
exit(1);
}
do
{
fflush(stdin); // Remove whitespace
printf_s("Enter a name less than %d characters: ", MAXLEN);
gets_s(name, sizeof(name)); // Read the name
printf_s("Enter the age of %s: ", name);
scanf_s(" %d", &age); // Read the age
// Write the name & age to file
length = strnlen_s(name, sizeof(name)); // Get name length
fwrite(&length, sizeof(length), 1, pfile); // Write name length
fwrite(name, sizeof(char), length, pfile); // then the name
fwrite(&age, sizeof(age), 1, pfile); // then the age
printf_s("Do you want to enter another(y or n)? " );
scanf_s("\n%c", &answer, sizeof(answer));
} while(tolower(answer) == 'y');
fclose(pfile); // Close the file
listfile(filename); // List the contents
return 0;
}
// List the contents of the binary file
void listfile(const char *filename)
{
size_t length = 0; // Name length
char name[MAXLEN]; // Stores a name
int age = 0;
char format[20]; // Format string
FILE *pfile = NULL;
// Create format string for names up to MAXLEN characters
sprintf_s(format, sizeof(format), "%%-%ds Age:%%4d\n", MAXLEN);
if(fopen_s(&pfile, filename, "rb")) // Open to read
{
printf_s("Failed to open file %s to read it.\n", filename);
exit(1);
}
printf_s("\nThe folks recorded in the %s file are:\n", filename);
// Read records as long as we read a length value
while(fread(&length, sizeof(length), 1, pfile) == 1)
{
if(length+1>MAXLEN)
{
printf_s("Name too long.\n");
exit(1);
}
fread(name, sizeof(char), length, pfile); // Read the name
name[length] = '\0'; // Append terminator
fread(&age, sizeof(age), 1, pfile); // Read the age
printf_s(format, name, age); // Output the record
}
fclose(pfile);
}
[/code]
