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file_write_read.c
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file_write_read.c
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/* https://cirosantilli.com/linux-kernel-module-cheat#c */
#include <lkmc.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>
/* Returns the size of the given open `FILE*`.
*
* If an error occurs, returns `-1L`.
*
* Does not work for pipes.
*/
long fget_file_size(FILE *fp) {
long oldpos;
long return_value;
oldpos = ftell(fp);
if (oldpos == -1L) {
return -1L;
}
if (fseek(fp, 0, SEEK_END) != 0) {
return -1L;
}
return_value = ftell(fp);
if (return_value == -1L) {
return -1L;
}
/* Restore the old position. */
if (fseek(fp, oldpos , SEEK_SET) != 0) {
return -1L;
}
return return_value;
}
/* Same as `file_size`, but takes the path instead of a `FILE*`. */
long file_size(char *path) {
FILE *fp;
long return_value;
fp = fopen(path, "r");
if (fp == NULL) {
return -1L;
}
return_value = fget_file_size(fp);
if (fclose(fp) == EOF) {
return -1L;
}
return return_value;
}
/* Read the entire file to a char[] dynamically allocated inside this function.
*
* Returns a pointer to the start of that array.
*
* In case of any error, returns NULL.
*
* http://stackoverflow.com/questions/174531/easiest-way-to-get-files-contents-in-c
*/
char *file_read(char *path) {
FILE *fp;
char *buffer;
long fsize;
fp = fopen(path , "rb");
if (fp == NULL) {
return NULL;
}
fsize = fget_file_size(fp);
if (fsize < 0){
fprintf(stderr, "could not determine lenght of:\n%s\n", path);
return NULL;
}
buffer = (char*)malloc(fsize);
if (buffer == NULL) {
return NULL;
}
if (fread(buffer, 1, fsize, fp) != (size_t)fsize) {
return NULL;
}
if (fclose(fp) == EOF){
return NULL;
}
return buffer;
}
/* Write a null terminated string to file
*
* Return -1 on failure, 0 on success.
*/
int file_write(char *path, char *write_string) {
long len;
FILE *fp;
fp = fopen(path, "wb");
if (fp == NULL) {
return -1;
}
len = strlen(write_string);
/* copy the file into the buffer: */
if (fwrite(write_string, 1, len, fp) != (size_t)len) {
return -1;
}
if (fclose(fp) == EOF) {
return -1;
}
return 0;
}
int main(void) {
char *path = LKMC_TMP_FILE;
char *data = "asdf\nqwer\n";
/* Write entire string to file at once. */
if (file_write(path, data) == -1) {
LKMC_IO_ERROR("file_write", path);
}
/* Read entire file at once to a string. */
{
char *output = file_read(path);
if (output == NULL) {
LKMC_IO_ERROR("file_read", path);
}
assert(strcmp(data, output) == 0);
free(output);
}
/* Get file size. */
{
long size = file_size(path);
if (size == -1) {
LKMC_IO_ERROR("file_size", path);
}
assert((size_t)size == strlen(data));
}
return EXIT_SUCCESS;
}