所以我试图在C中读取.bmp文件。我稍后将使用openssl库加密文件 - 但这只是背景信息。
我需要以二进制模式打开文件（显然），但无论出于何种原因，当我尝试打开文件时，它只读取4个字节。当我尝试输出我刚打开的这个确切的文件（用于错误测试）时，它输出以下内容 - 88 24 AD FB。
在我的故障排除中，我决定在文本文件（54字节）上尝试这个，我得到完全相同的结果。
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(){
char * fileName="pic_original.bmp";
//read the file from given filename in binary mode
printf("Start to read the .bmp file \n");
FILE *image;
image = fopen(fileName,"rb");
//print the size of the image (4 bytes every damn time)
printf("Size of image: %d\n",sizeof(image));
//output the exact file that was read (error testing)
FILE *test;
test = fopen("./test.bin", "w");
fwrite(image, sizeof(image), 1, test);
fclose(test);
fclose(image);
return 1;
}
这是图像（出于某种原因上传为png）
不完全确定我在哪里出错了，但我不是很喜欢C。
干杯，利亚姆
编辑1：
//allocate memory for the header and image
char *headerBuf = (char *)malloc(54);
char *imageBuf = (char *)malloc(sizeof(image)-54); //this line is wrong - thanks to user EOF
//allocate memory for the final ciphertext
char *imagecipherCBC = (char *)malloc(sizeof(image)); //wrong also
//read first 54 bytes (header)
rewind(image);
fread(headerBuf,54,1,image);
//read the bitmap image until the end of the file
fread(imageBuf,sizeof(image),1,image); //also wrong
那么，图像的大小当然是4个字节，它是32位机器上的文件指针。
我认为你必须准备一些bmp文件的图像缓冲区作为一个简单的例子，如果你的文件不是太大，你可以加密和解密这个图像缓冲区的内容。
static void read_from_image(char *imageBuf, int fileLength)
{
const char * outFileName="c:/DEV/temp/test.bin";
char headerBuf[54];
char *imagecipherCBC;
FILE *test;
test = fopen(outFileName, "wb");
//allocate memory for the final ciphertext
imagecipherCBC = (char *)malloc(fileLength *sizeof(char));
//read first 54 bytes (header)
//fread(headerBuf,54,1,image);
memcpy(headerBuf, imageBuf, 54 * sizeof(char));
//read the bitmap image until the end of the file
//fread(imageBuf,sizeof(image),1,image); //also wrong
fwrite(imageBuf, fileLength * sizeof(char), 1, test);
fflush(test);
fclose(test);
free(imagecipherCBC),imagecipherCBC = NULL;
free(imageBuf),imageBuf = NULL;
return;
}
您可以在主函数中拥有文件长度和图像缓冲区。
int main(int argc, char *argv[])
{
const char * fileName="c:/DEV/temp/pic_original.bmp";
int fileLength = 0;
FILE *image;
char *imageBuffer;
imageBuffer = NULL;
image = fopen(fileName,"rb");
printf("read the file from given filename in binary mode \n");
printf("Start to read the .bmp file \n");
//try to get a file length;
fseek(image, 0, SEEK_END);
fileLength = ftell(image);
fseek(image, 0, SEEK_SET);
rewind(image);
imageBuffer = (char*)malloc(fileLength * sizeof(char));
//print the size of the image (4 bytes every damn time)
printf("read the file from given filename in binary mode \n");
printf("Size of image file pointer: %d\n",sizeof(image));
printf("Size of image: %d\n",fileLength);
//output the exact file that was read (error testing)
fread(imageBuffer,sizeof(char),fileLength*sizeof(char), image);
fclose(image);
read_from_image(imageBuffer, fileLength);
return 0;
}
祝好运
如果您的目标是加密文件，则将整个文件读入缓冲区，加密并将其保存为二进制文件。您可以通过将文件指针移动到末尾来查找文件大小。例：
int main()
{
FILE *fin;
fin = fopen("pic_original.bmp", "rb");
fseek(fin, 0, SEEK_END);
int filesize = ftell(fin);
rewind(fin);
char *buf = malloc(filesize);
fread(buf, 1, filesize, fin);
fclose(fin);
//encrypt the buffer...
FILE *fout = fopen("output.bmp", "wb");
fwrite(buf, 1, filesize, fout);
fclose(fout);
return 0;
}
这适用于任何文件。 OpenSSL已经具有直接加密文件的功能。
如果由于某种原因你想保持标题相同，只改变后面的位，那么分别读取标题：
int main()
{
FILE *fin = fopen("input.bmp", "rb");
if(!fin) { printf("cannot open input\n"); return 0; }
FILE *fout = fopen("output.bmp", "wb");
if(!fout) { printf("cannot open output\n"); return 0; }
fseek(fin, 0, SEEK_END);
int filesize = ftell(fin);
if(filesize <= 54)
{
printf("wrong filesize\n");
return 0;
}
rewind(fin);
char *header = malloc(54);
char *buf = malloc(filesize - 54);
//encrypt buf...
fread(header, 1, 54, fin);
fread(buf, 1, filesize - 54, fin);
fclose(fin);
fwrite(header, 1, 54, fout);
fwrite(buf, 1, filesize - 54, fout);
fclose(fout);
free(header);
free(buf);
return 0;
}
我认为这样做的好处是加密的位图仍然会被识别为位图。但只有加密方法不会向输出添加额外的字节。
请注意，8位，4位和单色位图的调色板位于54字节标题之后，然后是图像位。