c - C编程将一定数量的字节打印到文件中

Question

可能重复：
C 编程将一定数量的字节打印到屏幕上

我想从一个文件中读取 partSize 数量的字节，该文件可以是任何类型，并将读取的相同数量打印到已经存在的新文件中。我写的程序似乎写得比想象的要少，并给出了分段错误。

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h> 
#include <sys/types.h> 
#define PERMS 0777
#include <errno.h>

int main()
{

int createDescriptor;
int openDescriptorOriginal;

int closeCreateDescriptor;

char fileNameOriginal[15]="picture.jpg";
//char fileNameOriginal[15]="myFile.txt";
//char fileNameNew[15]="NEWFILE.txt";
char fileName[15]="NEWFILE.jpg";

int parts;
int partSize;

parts=2;

int bytesRemaining;
int partNumber;

char BUFFER[512];

int readDescriptor;

int openDescriptor;

if ((openDescriptorOriginal = open(fileNameOriginal, O_RDONLY )) == -1)
 {
 printf("Error opening %s", fileNameOriginal);
 exit(EXIT_FAILURE);
 }

struct stat buf;
int r = fstat(openDescriptorOriginal, &buf);
if(r)
{
fprintf(stderr, "error: fstat: %s\n",(char *)strerror(errno));

exit(1);
}

int originalFileSize=buf.st_size;

printf("The file is %d Bytes large.\n",originalFileSize);

partSize=((originalFileSize+parts)-1)/parts;
printf("Each part is %.9f Kilobytes large.\n",(double)partSize/1024 );


partNumber=1;
printf("Part number: %d\n", partNumber);

if ((openDescriptor = open(fileName, O_WRONLY )) == -1)
{
printf("Error creating %s\n", fileName);
exit(EXIT_FAILURE);
}
ssize_t count, total;
total = 0;
char *bufff = BUFFER;
while (partSize) {
   count = read(openDescriptorOriginal, bufff, partSize);
    if (count < 0) {
       // handle error
        break;
    }
    if (count == 0)
        break;
    bufff += count;
    total += count;
    partSize -= count;
}
write (openDescriptor, BUFFER, total);
printf("\n");

    return 0;
}

Answer 1

一些初始问题：

• 将 CREAT 标志添加到您的 open() 以防文件不存在。
• 不应调整 partSize

取出调整 partSize 的线，它应该可以工作。

Answer 2

int bytesReceived;
.... open files ....
while ((bytesReceived = read(openDescriptorOriginal, BUFFER, sizeof(BUFFER)) > 0) {
    if (bytesReceived != write(openDescriptor, BUFFER, bytesReceived) {
        printError(...);
    }
}