Read the entire contents of a file to c char *, in

问题:

I'm looking for a cross platform (Windows + Linux) solution to reading the contents of an entire file into a char *.

This is what I've got now:

FILE *stream;
char *contents;
fileSize = 0;

//Open the stream
stream = fopen(argv[1], "r");

//Steak to the end of the file to determine the file size
fseek(stream, 0L, SEEK_END);
fileSize = ftell(stream);
fseek(stream, 0L, SEEK_SET);

//Allocate enough memory (should I add 1 for the \0?)
contents = (char *)malloc(fileSize);

//Read the file 
fscanf(stream, "%s", contents);     

//Print it again for debugging
printf("Read %s\n", contents);

Unfortunately this will only print the first line in the file so I assume that fscanf stops at the first newline character. However I would like to read the entire file including, and preserving, the new line characters. I'd prefer not to use a while loop and realloc to manually construct the entire string, I mean there has to be a simpler way?

回答1:

Something like this, may be?

FILE *stream;
char *contents;
fileSize = 0;

//Open the stream. Note "b" to avoid DOS/UNIX new line conversion.
stream = fopen(argv[1], "rb");

//Seek to the end of the file to determine the file size
fseek(stream, 0L, SEEK_END);
fileSize = ftell(stream);
fseek(stream, 0L, SEEK_SET);

//Allocate enough memory (add 1 for the \0, since fread won't add it)
contents = malloc(fileSize+1);

//Read the file 
size_t size=fread(contents,1,fileSize,stream);
contents[size]=0; // Add terminating zero.

//Print it again for debugging
printf("Read %s\n", contents);

//Close the file
fclose(stream);
free(contents);

回答2:

The function fread will read from the stream and not terminate on end-of-line characters.

From the man page, you have:

size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);

which reads in nitems of size size.

回答3:

fread reads all the files as-is:

 if (fread(contents, 1, fileSize, stream) != fileSize) {
    /* error occurred */
 }

回答4:

I've got this:

ssize_t filetomem(const char *filename, uint8_t **result)
{ 
    ssize_t size = 0;
    FILE *f = fopen(filename, "r");
    if (f == NULL) 
    { 
        *result = NULL;
        return -1;
    } 
    fseek(f, 0, SEEK_END);
    size = ftell(f);
    fseek(f, 0, SEEK_SET);
    *result = malloc(size);
    if (size != fread(*result, sizeof(**result), size, f)) 
    { 
        free(*result);
        return -2;
    } 

    fclose(f);
    return size;
}

Meaning of return value:

• Positive or 0: successfully read the file
• minus one: couldn't open file (possibly no such file)
• minus two: fread() failed