The following function accepts the name of a file as a string and returns the size of the file in bytes. If for any reason it cannot get the file information, it will return the value -1.
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In our header file, we used the following pre-processor directives around our declarations
#ifdef __cplusplus
extern "C" {
#endif
#ifdef __cplusplus } #endif
to allow c++ code to call our c function.
The usage example code makes three tests:
- Getting the size of the currently executing binary, as it will have a non-zero size
- Getting the size of a non-existing file, to check that it will properly return
-1 - Getting the size of an empty file, to be sure it is empty we create it right before the test
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Source file (file_helpers.c)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | #include <sys/stat.h>#include "file_helpers.h"//It will return the size of the file in bytes OR -1 in case that it cannot get any status information for itoff_t get_file_size(const char *filename) { //Specialised struct that can hold status attributes of files. struct stat st; //Gets file attributes for filename and puts them in the stat buffer. // Upon successful completion, it returns 0, otherwise and errno will be set to indicate the error. if (stat(filename, &st) == 0) { //Size of file, in bytes. return st.st_size; } return -1;} |
Header file (file_helpers.h)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | #ifndef GM_S_LITTLE_HELPERS_FILE_HELPERS_H#define GM_S_LITTLE_HELPERS_FILE_HELPERS_H#ifdef __cplusplusextern "C" {#endifoff_t get_file_size(const char *filename);#ifdef __cplusplus}#endif#endif //GM_S_LITTLE_HELPERS_FILE_HELPERS_H |
Usage example (main.cpp)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | #include <iostream>#include "file_helpers.h"void print_file_size(const char *filename) { const off_t size_of_file = get_file_size(filename); if (size_of_file > 0) { printf("The size of '%s' is %zd bytes\n", filename, size_of_file); } else if (size_of_file == 0) { printf("The file '%s' is empty\n", filename); } else { printf("Could not get the status information for file '%s'\n", filename); }}int main(int argc, char *argv[]) { //Testing a non-zero sized file print_file_size(argv[0]); //Testing for a non-existing file print_file_size("some file that does not exist..."); const char * filename = "/tmp/some_empty_file"; //Creating an empty file FILE * fout = fopen(filename, "w"); fclose(fout); //Testing for an empty file print_file_size(filename); return 0;} |
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