在Mac上的Xcode中使用fopen（fileName，“ wb”）之后无法访问我的二进制文件

Question

FILE* inFile = fopen(inF, "rb");
if (inFile == NULL) {
    printf("Invalid input!\n");
    exit(EXIT_FAILURE);
}

char* bigBuffer;
char* nextChar = (char*) malloc(sizeof(char));
unsigned long i = 0;
unsigned long j;
while ((j = fread(nextChar, sizeof(char), 1, inFile)) == 1) {
    i += j;
}
bigBuffer = malloc(i * sizeof(char));
fread(bigBuffer, sizeof(char), i, inFile);
fclose(inFile);
printf("%s\n", outF);
FILE* outFile = fopen(outF, "wb");
//if (outFile == NULL)
    //printf("null\n");
j = fwrite(bigBuffer, sizeof(char), i, outFile);
printf("%lu\n", j);
fclose(outFile);
free (bigBuffer);
free (nextChar);

I'm trying to write a binary file using fopen in wb mode. After running my program, a file of the proper name is made in the proper place, but I just can't open it or read it. When I try to open it, a message pops up saying "Can't open...." In addition, the name of the file itself isn't formatted properly in Finder (I'm on a Mac). The name is elevated and cut off a little. It definitely looks like something is wrong with the file. I tried just making a regular file using fopen in w mode, and that worked beautifully. So I'm pretty sure I'm just doing something wrong when it comes to writing binary files using wb mode. Can anyone help? Thanks.

Answer 1

The main problem:

• you didn't seek to the beginning of the file before reading, so your call to fread to read the entire file will fail

Change:

bigBuffer = malloc(i * sizeof(char));
fread(bigBuffer, sizeof(char), i, inFile);

to:

bigBuffer = malloc(i);              // allocate buffer
rewind(inFile);                     // reset file pointer to start of file
fread(bigBuffer, 1, i, inFile);     // read entire file

Additional notes:

• sizeof(char) is 1 by definition, and therefore redundant
• you should not cast the result of malloc in C
• you should add error checking to any call that might fail, especially I/O calls
• malloc -ing a single char is inefficient - just use a local variable
• reading a file one char at a time to determine its length is very inefficient

Answer 2

The file with the opening in wb truncated to 0 length. Use for simultaneous read / write mode or addition mode rb +, a.