Write bitstream to file in C - c

Question

I'm currently trying to use a CMP decompressor: https://web.archive.org/web/20070113004119/http://rewiki.regengedanken.de:80/wiki/.CMP
It does in fact decompress the cmp, but it does not write it into a file.
So i tried myself.
int main(int argc, char** argv)
{
int length, dstLength;
unsigned char* fileInMem; //compressed data
unsigned char* dstFile; //decompressed data
if (argc < 2) {
fprintf(stderr, "give filename.cmp as parameter\n");
return 1;
}
printf("%s", argv[1]);
fileInMem = loadFile(argv[1], &length); //compressed data read
if (fileInMem == NULL) {
return 1;
}
dstFile = parseCmp(fileInMem, length, &dstLength); //decompress and assign data to dstFile
if (dstFile) {
/* Now we can save the file from dstFile, dstLength bytes */
printf("%d bytes depacked\n", dstLength);
for (int i = 0; i < 16; i++) {
dataArray[i] = fileInMem[i];
}
FILE *writer = fopen(argv[2], "r+");
//fputs(fileInMem, writer);
//fputs(dstFile, writer);
fclose(writer);
free(dstFile);
}
free(fileInMem);
return 0;
}
As you can see the decompressed data is a pointer to an unsigned char (according to the website a bitstream) and I tried fputs() from stdio.h, but the resulting file contains only 4 Bytes when viewed in a hex-editor.
If you need more information, please comment.
Thank you in advance.
Edit: This is what I was able to change thanks to your help, but when I open the file, it is still empty:
FILE* writer = fopen(argv[2], "wb");
fwrite(dstFile, 192, 192, writer);
192, because the length of the first decompressed Image is 192 Bytes large.

Answer 1

This is a common issue.
First, you need to open the output file writer for writing in binary mode ("wb").
FILE *writer = fopen(argv[2], "wb");
Second, you can't use fputs to write arbitrary data to a file, since it expects a string. Use fwrite instead: (assuming writer is the output file, dstFile the decompressed data and dstLength the amount of bytes to write)
fwrite(dstFile, 1, dstLength, writer);
If you examine the resulting file with an hex editor, you will see it is identical to the decompressed data.
Test-update
I wrote some test-code to see what is wrong, share your results so we can help you.
Add these functions to your code:
void printDataToScreen(unsigned char *dataptr, int datalen)
{
if (dataptr == NULL)
{
printf("[!] ERROR, NULL POINTER PROVIDED!\n");
return;
}
printf("> Dumping %d bytes of data into the terminal...\n", datalen);
for (int i = 0; i < datalen; i++)
{
if (i % 16 == 0)
printf("\n ");
printf("%02X ", dataptr[i]);
}
printf("\n\n");
}
void writeDataToFile(char *fileName, unsigned char *dataptr, int datalen)
{
FILE *file = fopen(fileName, "wb");
if (dataptr == NULL)
{
printf("[!] ERROR, NULL POINTER PROVIDED!\n");
return;
} else if (file == NULL)
{
printf("[!] ERROR WHILE OPENING FILE '%s'!\n", fileName);
return;
}
printf("> Writting %d bytes of data to '%s'...\n", datalen, fileName);
int writtenBytes = fwrite(dataptr, 1, datalen, file);
printf(" Done, %d bytes written!\n\n", writtenBytes);
fclose(file);
}
void runTest(char *fileName, unsigned char *dataptr, int datalen)
{
printf("Running tests... [0/2 done]\n");
printDataToScreen(dataptr, datalen);
printf("Running tests... [1/2 done]\n");
writeDataToFile(fileName, dataptr, datalen);
printf("Finished! [2/2 done]\n");
}
Call it like this:
runTest(argv[2], dstFile, dstLength);
Add the call to this place in your code (comment this code, also the line where you close writer):
FILE *writer = fopen(argv[2], "r+");
//fputs(fileInMem, writer);
//fputs(dstFile, writer);
Please share your results.