C 将带有 memcpy 和 mmap 文件的文件复制到 RAM

Question

我有 file1.txt

This is my file

和file2.txt

This is my second file

我想使用 memcpy 将 file2.txt 内容复制到 file1.txt

int main( int argc, char * argv[] ){
    int d;
    int d2;
    int p;
    FILE *f1;
    FILE *f2;
    if(argc == 3){
        f1 = fopen(argv[1], "r+");
        f2 = fopen(argv[2], "r+");
            d = da_open(argv[1]);
            d2 = da_open2(argv[2]);
            p = da_cp(f2, f1, 10); 
            da_map(d, 10);
            da_map(d2, 10);

            close(p);
            //closef(d2);
    }

}我不知道为什么，但是当我运行这个程序时，我得到带有很多随机符号的 file2.txt 。为什么？我做错了什么？

编辑:我的完整代码

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/time.h>
#include <string.h>

int da_open(const char *name);
int da_open2(const char *name);
void *da_map(int d, int size);
int da_cp(void *str1, const void *str2, size_t n);

int da_open(const char *name){
   int dskr;
   dskr = open( name, O_RDONLY, 0640 );
   if( dskr == -1 ){
      perror( name );
      exit( 255 );
   }
   printf( "dskr = %d\n", dskr );
   return dskr;
}

int da_open2(const char *name){
   int dskr;
   dskr = open( name, O_RDWR, 0640 );
   if( dskr == -1 ){
      perror( name );
      exit( 255 );
   }
   printf( "dskr = %d\n", dskr );
   return dskr;
}

void *da_map(int d, int size){
   void *a = NULL;
   a = mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, d, 0 );
   if( a == MAP_FAILED ){
      perror( "mmap failed" );
      abort();
   }
   return a;
}

int da_cp(void *str1, const void *str2, size_t n){
         memcpy(str1, str2, n);
}

int main( int argc, char * argv[] ){
        int d;
        int d2;
        int p;
        FILE *f1;
        FILE *f2;
        if(argc == 3){
            f1 = fopen(argv[1], "r+");
            f2 = fopen(argv[2], "r+");
                d = da_open(argv[1]);
                d2 = da_open2(argv[2]);
                 p = da_cp(f2, f1, 10);
                da_map(d, 10);
                da_map(d2, 10);

                close(p);
                //closef(d2);
        }
}

Answer 1

d 和 d2 不是文件，它们只是文件描述符(存储有关文件及其输入/输出状态的信息)。

如果您想从一个文件复制到另一个文件，则必须先读取第一个文件。这是如何执行此操作的示例:

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

// Open the first text file
FILE *f = fopen("textfile1.txt", "rb");
fseek(f, 0, SEEK_END);
long fsize = ftell(f);
fseek(f, 0, SEEK_SET);

// Read it into buffer
char *buffer = malloc(fsize + 1);
fread(string, fsize, 1, f);
fclose(f);

buffer[fsize] = 0;

// Now write the string buffer into your second text file
FILE *f2 = fopen ("textfile2", "wb");
fwrite (buffer, sizeof(char), sizeof(buffer), f2);
fclose (f2);

因此，如您所见，memcpy 只能在 RAM 中的内存中执行，与硬盘驱动器中的文件无关(除非您将其读入 RAM 内存)