c / intermediate
Snippet
Determining File Size with fseek and ftell
To measure a file's size without reading every byte, you can seek to the end of the stream and query the position. This is essential for allocating exactly enough memory to load a file's content into a buffer.
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#include <stdio.h>long get_file_size(const char *path) {FILE *file = fopen(path, "rb");if (!file) return -1;fseek(file, 0L, SEEK_END); // Move pointer to endlong size = ftell(file); // Get current offsetfclose(file);return size;}int main(void) {long bytes = get_file_size("example.bin");if (bytes != -1) printf("File size: %ld bytes\n", bytes);return 0;}
Breakdown
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fseek(file, 0L, SEEK_END)
Sets the file position indicator to the very end of the file.
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ftell(file)
Returns the current value of the position indicator (number of bytes from start).