ccharts

Financial OHLC data in, a string out. Line and candlestick charts drawn with Unicode block characters and returned as text — so the chart goes wherever text goes: a terminal, a log line, a chat message, an HTML <pre>, a commit comment, a .txt file, a printf.

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2026-07-20                                                2026-07-24

Color is optional: by default rising and falling segments carry ANSI escapes, and plain renders with none at all, for the destinations where escapes would only be noise.

There is no canvas, no image, no renderer to drive and nothing to draw into — one call returns a string, and what you do with it is your business.

Written as a single-header C library with a flat C ABI and bindings for Python, Rust, Go, JavaScript, C# and Java. Every one of them produces byte-identical output.

Licensed under the MIT License.

Installation

pip install ccharts

For pandas DataFrame support (optional — the package itself has no runtime dependencies):

pip install ccharts[pandas]

Pre-built wheels for Linux (x86_64 and aarch64), macOS (x86_64 and arm64) and Windows (x86_64), built on GitHub Actions CI for CPython 3.9-3.14, are published together with each release — no C toolchain is needed on the target machine. Install the sdist instead and a C compiler (gcc/Clang on Linux/macOS, MSVC on Windows) is required, because the package wraps the C single-header library ccharts.h.

Features

• Strings, not output — every entry point returns a string. Nothing is printed, no stream is written to, no terminal is detected or resized around.
• Plain or colored — plain yields text with no ANSI escapes at all; otherwise colors are escape strings you choose, including 256-color and truecolor.
• Line charts — smooth curves using 8-level vertical resolution (▁▂▃▄▅▆▇█), per-segment coloring, optional area fill under the line.
• Candlestick charts — solid bodies between open/close, thin vertical wicks (│) between high/low, gap-separated candles, automatic downsampling when there are more candles than columns.
• Axis labels — optional max/min price margin and first/last timestamp footer. The timestamp format is picked automatically from the candle interval (YYYY-MM-DD for daily+, HH:MM for intraday).
• Timestamps — optional per-candle epoch timestamps, parsed from ISO8601 or a plain number.
• Parsers — CSV (cc_str_to_ohlc) and a fixed-schema JSON parser (cc_json_to_ohlc).
• pandas / columnar input (Python) — Chart.from_dataframe(df) and Chart.from_arrays(...) copy price columns straight into the C array, with no JSON round-trip. pandas is optional.

C usage

#define CCHARTS_IMPLEMENTATION
#include "ccharts.h"

int main(void) {
    const char* json = ...;                 // [{ts,open,high,low,close}, ...]
    cc_ohlc_t* ohlc = NULL;
    int size = 0;
    cc_json_to_ohlc(json, &ohlc, &size);

    cc_settings_t s = { .rise_color = CC_COLOR_BLUE,
                        .show_prices = 1, .show_times = 1 };
    char* chart = cc_line_create(ohlc, size, 60, 8, &s);
    printf("%s\n", chart);

    free(chart);
    free(ohlc);
    return 0;
}

cc_line_create hands back a char* you own: print it, log it, embed it, free() it. Compile with -lm (math lib). CCHARTS_IMPLEMENTATION must be defined in exactly one translation unit; every other unit can include the header as-is. C++ code can use the header for declarations (see the doc comment in ccharts.h for details).

Run the demo with make test — it compiles main.c and runs the binary, rendering prices.txt as a line chart and two candlestick variants.

Python usage

make test-py        # builds the extension and runs the test suite

from ccharts import Chart

chart = Chart(open("prices.txt").read())
print(chart.line(width=60, height=8, show_prices=True, show_times=True))
print(chart.candle(width=60, height=8))

DataFrames and raw columns

A DataFrame does not have to be serialized to JSON first — the price columns are handed to C directly:

import yfinance as yf
from ccharts import Chart

df = yf.download("THYAO.IS", period="3mo")     # Open/High/Low/Close columns
print(Chart.from_dataframe(df).candle(width=80, height=12, show_times=True))

• Columns are matched case-insensitively (Open/open/OPEN); pass ohlc=("o", "h", "l", "c") for anything else.
• Timestamps come from a DatetimeIndex, or from ts="column". Timezone-aware values are converted to UTC, naive ones are treated as UTC.
• Rows with NaN/inf in an OHLC column are dropped (indicator frames have NaN warm-up rows); dropna=False raises instead.
• Row order is used as-is — a descending frame renders right to left.

The same path works without pandas, for lists, numpy arrays or array.array:

Chart.from_arrays(opens, highs, lows, closes, ts=epoch_seconds)

To develop locally (builds the extension in place):

python3 -m pip install -e .      # or: make test-py

Building a wheel by hand also works and is a good local smoke test:

python3 -m pip wheel . --no-deps -w /tmp/ccharts_wheel

C ABI and other languages

ccharts.h exports nothing — CC_INLINE makes every function static inline, and struct cc_ohlc is private to the implementation block — so there is nothing for a foreign function interface to bind to. abi/ccharts_abi.h provides that layer: a flat, extern "C", opaque-handle API with explicit status codes, built as a shared or static library.

cmake -S . -B build && cmake --build build
ctest --test-dir build --output-on-failure

#include "ccharts_abi.h"

ccharts_data* data = NULL;
ccharts_from_arrays(open, high, low, close, ts, n, &data);

ccharts_settings s = {0};
s.rise_color = ccharts_color(CCHARTS_COLOR_BLUE);
s.show_prices = 1;

char* chart = NULL;
size_t len = 0;
if (ccharts_line(data, 60, 8, &s, &chart, &len) == CCHARTS_OK) {
    printf("%s", chart);
    ccharts_string_free(chart);
}
ccharts_data_free(data);

Differences from the raw header, all in the direction of being bindable: invalid dimensions return CCHARTS_ERR_DIMENSIONS instead of an empty string, NaN and inf are rejected up front, and ccharts_parse_csv counts the rows it can parse so a dataset never carries trailing zero-filled candles.

conformance/cases.json plus conformance/golden/*.txt are the cross-language contract: 20 cases covering both chart types, downsampling, labels, timezones, flat ranges and single-candle input. The goldens are generated from the ABI (scripts/gen_golden.py) and every binding — the Python one included, see tests/test_conformance.py — must reproduce them byte for byte.

Language bindings

Rust and Go compile the vendored C sources with their own toolchains (the cc crate and cgo), so neither needs a prebuilt library:

let chart = Chart::from_arrays(&open, &high, &low, &close, Some(&ts))?;
println!("{}", chart.line(60, 8, &Settings::new().rise(Color::Blue))?);

chart, _ := ccharts.FromArrays(open, high, low, close, ts)
defer chart.Close()
out, _ := chart.Candle(60, 8, &ccharts.Options{ShowPrices: true})

The JavaScript package is the library compiled to WebAssembly, with the module embedded in the JavaScript — one dependency-free package for Node, Deno, Bun and browsers alike, no prebuilt binaries and no bundler configuration:

import { Chart, Color } from "@dethrandir/ccharts";
const chart = Chart.fromArrays(open, high, low, close, ts);
console.log(chart.candle({ width: 60, height: 8, showPrices: true }));
chart.free();

C# uses source-generated P/Invoke and Java the Foreign Function & Memory API (no JNI code at all). Both link the shared library rather than compiling the C, so both ship prebuilt natives — runtimes/{rid}/native/ in the NuGet package, native/{os}-{arch}/ in the jar:

using var chart = Chart.FromArrays(open, high, low, close, ts);
Console.Write(chart.Line(new ChartOptions { RiseColor = Color.Blue, ShowPrices = true }));

try (Chart chart = Chart.fromArrays(open, high, low, close, ts)) {
    System.out.print(chart.line(ChartOptions.builder().rise(Color.BLUE).build()));
}

Each binding vendors its own copy of ccharts.h and the ABI — Go needs cgo sources inside the package directory and cargo package only ships crate-local files — so scripts/sync_sources.py refreshes them and CI fails if a copy drifts.

Settings

Setting a color to the empty string (rather than leaving it unset) makes that element carry no escape sequence at all — no color, and no reset either. Set all four and the chart comes out as plain text. The bindings expose that as a single plain option:

chart.line(width=60, height=8, plain=True)   # not one escape byte

Any unset field falls back to its default, so only the fields you want to override need to be set (see cc_settings_resolve).

Input constraints

• Timestamps — ISO8601 strings may carry a UTC offset (+03:00, +0300, +03, Z; a missing offset is treated as UTC). The offset is applied, so the stored epoch is the true instant: 2026-07-20T00:00:00+03:00 becomes 2026-07-19T21:00:00 UTC. Plain epoch-seconds numbers (including negative) are accepted as-is. Malformed timestamps parse to 0.
• Dimensions — width/height must be positive and are capped at CC_MAX_DIM (100000) per side and CC_MAX_CELLS (1000000) total cells. Invalid dimensions make the C chart functions return an empty string and make the Python bindings raise ValueError — no unchecked giant allocation, no stack overflow.
• CSV — lines may be arbitrarily long and at most size lines are read.
• JSON — must be an array of objects with ts, open, high, low, close (plus optional ignored fields like volume). The parser is an iterative mini-scanner: keys are matched exactly, so a substring like "open" inside a string value can never cause a false match. Malformed or empty documents make the parsers fail cleanly.

Windows / MSVC

The header is VLA-free and uses only portable C89 constructs, so it compiles with MSVC out of the box: gmtime_r is swapped for gmtime_s on _WIN32 and all functions get internal linkage (static) through the CC_INLINE macro, sidestepping MSVC's lack of C11 inline semantics. No extra flags or libraries are required beyond the standard ones.

Releases

One tag releases everything. Pushing v<version> (e.g. v0.2.0) runs .github/workflows/publish.yml, which first refuses the build unless the tag and every manifest agree on the version (scripts/check_versions.py), then publishes each package. Each registry's credential (API token, username, GPG key) is expected as a GitHub repository secret and is documented in the workflow, not here:

The Go module has no registry — it is served from the repository — but a module in a subdirectory needs a tag carrying that prefix, so the workflow also pushes bindings/go/v<version>.

The C# and Java packages are the only ones carrying binaries: .github/workflows/natives.yml builds the shared library for linux-x64, osx-arm64 and win-x64, and scripts/pack_natives.py arranges them into runtimes/{rid}/native/ for NuGet and native/{os}-{arch}/ for the jar. Both publish jobs then verify the packed artifact actually contains every platform before it leaves the runner — a package that quietly lost its natives would install fine and fail on the first call. (Linux aarch64 is not built, for the same reason the Python wheels skip it: QEMU emulation on GitHub-hosted runners is far too slow. It can be added once native ARM runners are available.)

workflow_dispatch runs every build job without uploading anything, so a release can be rehearsed in full.

Two notes on publishing: PyPI could drop its API token entirely by moving to trusted publishing — link the pypi GitHub environment and delete the password input. Maven Central requires a verified io.github.dethrandir namespace on the Central Portal and a published GPG key before the first deploy will be accepted.

Repository layout

• ccharts.h — the whole C library (single header, heavily documented).
• main.c — C demo using prices.txt.
• prices.txt — sample JSON OHLC data (THYAO).
• abi/ — flat C ABI (ccharts_abi.h/.c) for non-Python bindings.
• bindings/ — language bindings built on that ABI (rust/, go/, js/, dotnet/, java/).
• conformance/ — cross-language case list, goldens and a C smoke test.
• scripts/ — golden generation, vendored-source sync, version consistency.
• ccharts/ — Python package: __init__.py (high-level Chart), wrapper.c (CPython extension ccharts._core) and _pandas.py (optional DataFrame conversion, imported lazily).
• tests/ — Python test suite (test_python_api.py, plus test_pandas_api.py which skips when pandas is not installed).