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Office Oxide

C / FFI Office Library — Quick Start

The office_oxide C API is a stable, thin ABI over the Rust core. All higher-level bindings (Go, C#, Node.js native) call these same entry points, so if your language doesn’t have a ready-made wrapper you can always link the C library directly.

The authoritative surface lives in include/office_oxide_c/office_oxide.h; this guide walks through the same API.

Install

Option 1 — build from Rust source

git clone https://github.com/yfedoseev/office_oxide
cd office_oxide
cargo build --release --lib

The shared library lands under target/release/:

OS File
Linux liboffice_oxide.so
macOS liboffice_oxide.dylib
Windows office_oxide.dll (+ .lib import library)

The header lives at include/office_oxide_c/office_oxide.h.

Option 2 — install a prebuilt library

install -Dm644 include/office_oxide_c/office_oxide.h /usr/local/include/office_oxide.h
install -Dm755 target/release/liboffice_oxide.so     /usr/local/lib/liboffice_oxide.so

Read a document

#include <stdio.h>
#include <stdlib.h>
#include "office_oxide.h"

int main(void) {
    int err = 0;
    char *text = office_extract_text("report.docx", &err);
    if (!text) {
        fprintf(stderr, "office_oxide failed: code=%d\n", err);
        return 1;
    }
    printf("%s\n", text);
    office_oxide_free_string(text);
    return 0;
}

Build and run:

cc quickstart.c -I/usr/local/include -L/usr/local/lib -loffice_oxide -o quickstart
LD_LIBRARY_PATH=/usr/local/lib ./quickstart

Core API

Library info

const char *version = office_oxide_version();          // "0.1.0" — don't free
const char *fmt     = office_oxide_detect_format("f"); // "docx"/... or NULL

Document (read-only)

int err = 0;
OfficeDocumentHandle *doc = office_document_open("file.xlsx", &err);
if (!doc) { /* handle err */ }

const char *fmt = office_document_format(doc);         // "xlsx" — don't free

char *text = office_document_plain_text(doc, &err);
char *md   = office_document_to_markdown(doc, &err);
char *html = office_document_to_html(doc, &err);
char *ir   = office_document_to_ir_json(doc, &err);

if (office_document_save_as(doc, "file.docx", &err) != 0) {
    /* handle err */
}

office_oxide_free_string(text);
office_oxide_free_string(md);
office_oxide_free_string(html);
office_oxide_free_string(ir);

office_document_free(doc);

Open from an in-memory buffer:

uint8_t *data = ...;
size_t   len  = ...;
OfficeDocumentHandle *doc =
    office_document_open_from_bytes(data, len, "docx", &err);

format must be one of the six strings "docx" | "xlsx" | "pptx" | "doc" | "xls" | "ppt".

EditableDocument

Editing preserves every unmodified OPC part on save. DOCX, XLSX, and PPTX only.

int err = 0;
OfficeEditableHandle *ed = office_editable_open("template.docx", &err);
if (!ed) { /* handle err */ }

int64_t n = office_editable_replace_text(ed, "{{name}}", "Alice", &err);
if (n < 0) { /* handle err */ }
printf("%lld replacements\n", (long long)n);

if (office_editable_save(ed, "out.docx", &err) != 0) {
    /* handle err */
}

office_editable_free(ed);

Set XLSX cells:

OfficeEditableHandle *wb = office_editable_open("budget.xlsx", &err);

office_editable_set_cell(wb, 0, "A1", OFFICE_CELL_STRING, "Total", 0.0,  &err);
office_editable_set_cell(wb, 0, "B1", OFFICE_CELL_NUMBER,  NULL,   42.5, &err);
office_editable_set_cell(wb, 0, "C1", OFFICE_CELL_BOOLEAN, NULL,   1.0,  &err);
office_editable_set_cell(wb, 0, "D1", OFFICE_CELL_EMPTY,   NULL,   0.0,  &err);

office_editable_save(wb, "budget.xlsx", &err);
office_editable_free(wb);

For booleans, non-zero value_num = true.

Serialize to a heap buffer:

size_t   out_len = 0;
uint8_t *buf     = office_editable_save_to_bytes(ed, &out_len, &err);
if (!buf) { /* handle err */ }
/* upload or stream buf[0..out_len] */
office_oxide_free_bytes(buf, out_len);

One-shot helpers

char *text = office_extract_text("file.docx", &err);
char *md   = office_to_markdown("file.pptx", &err);
char *html = office_to_html("file.xlsx", &err);
/* free each with office_oxide_free_string */

Memory rules

  • Strings returned as char* from office_document_*, office_editable_*, and the one-shot helpers must be freed with office_oxide_free_string(ptr).
  • Byte buffers returned as uint8_t* (with an out_len out-parameter) must be freed with office_oxide_free_bytes(ptr, len). The len must match the value the API wrote to out_len.
  • Opaque handles must be freed with their matching *_free() call.
  • const char* values from office_oxide_version, office_oxide_detect_format, and office_document_format are static — do not free.

Errors

Every fallible call takes an int *error_code out-parameter:

int err = 0;
OfficeDocumentHandle *doc = office_document_open("missing.docx", &err);
if (!doc) {
    switch (err) {
        case OFFICE_ERR_IO:    fputs("io error\n", stderr); break;
        case OFFICE_ERR_PARSE: fputs("parse error\n", stderr); break;
        /* ... */
    }
}
Macro Value Meaning
OFFICE_OK 0 success
OFFICE_ERR_INVALID_ARG 1 nil pointer / unknown format string
OFFICE_ERR_IO 2 filesystem error
OFFICE_ERR_PARSE 3 malformed document
OFFICE_ERR_EXTRACTION 4 parsed but rendering failed
OFFICE_ERR_INTERNAL 5 bug — please file an issue
OFFICE_ERR_UNSUPPORTED 6 extension / feature not supported

Cell value constants

Macro Value
OFFICE_CELL_EMPTY 0
OFFICE_CELL_STRING 1
OFFICE_CELL_NUMBER 2
OFFICE_CELL_BOOLEAN 3

Legacy formats

Open with office_document_open — extension drives format detection, magic bytes verify it. office_document_save_as converts legacy → OOXML transparently:

OfficeDocumentHandle *doc = office_document_open("old.xls", &err);
office_document_save_as(doc, "modern.xlsx", &err);
office_document_free(doc);

Thread safety

Each handle is owned by the caller — do not share a single handle between threads. Different handles can be used in parallel; the library itself is reentrant.

C++

The header is wrapped in extern "C" guards, so it drops straight into a C++ translation unit:

#include "office_oxide.h"

Pair with RAII wrappers (std::unique_ptr<OfficeDocumentHandle, decltype(&office_document_free)>) to make cleanup exception-safe.

Troubleshooting

Symptom Fix
Linker: undefined reference to office_document_open Add -loffice_oxide and a matching -L flag; ensure the library was built --release --lib.
Runtime: error while loading shared libraries: liboffice_oxide.so Add the library directory to LD_LIBRARY_PATH (Linux), DYLD_LIBRARY_PATH (macOS), or next to the exe (Windows).
OFFICE_ERR_INVALID_ARG on open_from_bytes format must be exactly `“docx”
Double-free or heap corruption Free each char* with office_oxide_free_string, each byte buffer with office_oxide_free_bytes(ptr, len) using the original out_len.
office_editable_replace_text returns 0 on XLSX Expected — use office_editable_set_cell for spreadsheet edits.

See also