JSON Output

The gcovr command can also generate a JSON output using the --json and --json-pretty options:

gcovr --json coverage.json

The --json-pretty option generates an indented JSON output that is easier to read.

If you just need a summary of the coverage information, similar to the tabulated text based output, you can use --json-summary instead (see JSON Summary Output).

Multiple JSON files can be merged into the coverage data with sum of lines and branches execution, see Merging Coverage Data.

See the JSON Format Reference for a description of the file format.

Changed in version 8.0: Order of keys changed from alphabetical to logical.

JSON Format Reference

The structure of the JSON input/output files is based on the GCC gcov JSON intermediate format, but with additional keys specific to gcovr. Field names use snake_case. Gcovr-specific fields are prefixed with gcovr/....

The GCC gcov JSON format is documented at https://gcc.gnu.org/onlinedocs/gcc-14.1.0/gcc/Invoking-Gcov.html.

The top level of the file looks like the following:

{
    "gcovr/format_version": version,
    "files": [file]
}

gcovr/format_version: string

A version number string for the gcovr JSON format. This is versioned independently from gcovr itself. Consumers of gcovr JSON reports should check that they are SemVer-compatible with the declared version. Gcovr itself will only consume input files that match the exact version.

Current version is:

“0.11”

files: list

An unordered list of file entries.

File entries

Each file entry contains coverage data for one source file:

{
    "file": filename,
    "lines": [line],
    "functions": [function]
    "gcovr/data_sources": [data_sources]
}

file: string: Path to the source code file. If the source file is within the gcovr root directory, the path will be relative.
lines: list: An unordered list of line coverage entries.
functions: list: An unordered list of function entries.
gcovr/data_sources: list: A list of files from which the coverage object was populated. This entry is only available if --verbose is given.

Line entries

Each line entry contains coverage data for one line:

{
    "line_number": line_number,
    "function_name": function_name,
    "count": count,
    "branches": [branch],
    "block_ids", block_ids,
    "conditions", conditions
    "gcovr/md5": md5,
    "gcovr/excluded": excluded,
    "gcovr/decision": decision
    "gcovr/calls": calls,
}

line_number: int: The 1-based line number to which this entry relates.
function_name: str: Only available if gcov JSON format is used it contains the name of the function to which the line belongs to. Can be missing for a line with an inlined statement.
count: int: How often this line was executed.
branches: list: A list of branch coverage entries.
conditions: list: Only available if GCOV JSON format is used it contains a list of branch coverage entries.
block_ids: list[int]:: The list of block ids defined in this line.
gcovr/md5: str: The MD5 sum of the line.
gcovr/excluded: boolean: True if coverage data for this line was explicitly excluded, in particular with Exclusion Markers. May be absent if false.
gcovr/decision: object: The decision entry for this line, if any. Absent if there is no decision to report. Requires that --decisions coverage analysis was enabled.
gcovr/calls: object: The call for this line, if any. Absent if there is no call to report. Requires that --calls coverage analysis was enabled.

If there is no line entry for a source code line, it either means that the compiler did not generate any code for that line, or that gcovr ignored this coverage data due to heuristics.

The line entry should be interpreted as follows:

if gcovr/excluded is true, the line should not be included in coverage reports.
if count is 0, the line is uncovered
if count is nonzero, the line is covered

Changed in version 8.0: The conditions is added.

Changed in version 8.0: The block_ids is added.

Changed in version 8.0: The function_name is added.

Changed in version 8.0: The gcovr/md5 is added.

Changed in version 6.0: The gcovr/excluded field can be absent if false.

Changed in version 6.0: The gcovr/noncode field was removed. Instead of generating noncode entries, the entire line is skipped.

Branch entries

Each branch provides information about a branch on that line:

{
  "count": count,
  "fallthrough": fallthrough,
  "throw": throw,
  "source_block_id": number,
  "destination_block_id": number
}

This exactly matches the GCC gcov format.

count: int: How often this branch was taken.
fallthrough: boolean: Whether this is the “fallthrough” branch.
throw: boolean: Whether this is an exception-only branch.
source_block_id: int: The source block of this branch.
destination_block_id: int: The destination block of this branch. Only available if gcov JSON format is used.

Added in version 8.0: Added destination_blockno field.

Added in version 8.3: Added source_block_id field.

Changed in version 8.3: Renamed destination_blockno to destination_block_id field.

Condition entries

Each condition provides information about a condition on that line:

{
  "count": count,
  "covered": covered,
  "not_covered_false": not_covered_false,
  "not_covered_true": not_covered_true
}

This exactly matches the GCC gcov format.

count: int: Number of condition outcomes in this expression.
covered: int: Number of covered condition outcomes in this expression.
not_covered_false: list[int]: Terms, by index, not seen as false in this expression.
not_covered_true: list[int]: Terms, by index, not seen as true in this expression.

Decision entries

Each decision summarizes the line’s branch coverage data:

{
  "type": "uncheckable"
}

{
  "type": "conditional",
  "count_true": count_true,
  "count_false": count_false
}

{
  "type": "switch",
  "count": count
}

type: string

A tag/discriminator for the type of the decision.

type: “uncheckable”

Control flow was recognized on this line, but cannot be interpreted unambiguously.

No further fields.

type: “conditional”

This line represents simple control flow like an if or while.

count_true: int: How often the decision evaluated to “true”.
count_false: int: How often the decision evaluated to “false”.

Note that the true/false are heuristic guesses, and might also be inverted.

type: “switch”

This line is a switch-case.

count: int: How often this case was taken.

Call entries

Each call provides information about a call on that line:

{
  "callno": callno,
  "covered": covered
}

callno: int: The number of the call.
covered: boolean: Whether this call was covered.

Function entries

Each function entry describes a line in the source file:

{
  "name": name,
  "demangled_name": demangled_name,
  "lineno": lineno,
  "execution_count": count,
  "branch_percent": percent,
  "pos": [
    "<start line>:<start column>",
    "<end line>:<end column>"
  ]
  "gcovr/excluded": excluded
}

name: string: The name of the function. If legacy gcov text output is used it contains the demangled name if supported by the gcov tool except for clang-10 where the mangled name is used. If gcov JSON format is used it always contains the mangled name.
demangled_name: string: Only available if GCOV JSON format is used it always contains the demangled name.
lineno: int: The line number (1-based) where this function was defined. Incompatible with GCC gcov JSON.
execution_count: int: How often this function was called.
branch_percent: float: The branch coverage in percent (0.0 to 100.0).
pos: list: A list with start and end position of function (1-based). Both entries are string with line and column separated by :. Only available if gcov JSON format is used.
gcovr/excluded: boolean: True if coverage data for this function was explicitly excluded, in particular with Exclusion Markers. May be absent if false.

if gcovr/excluded is true, the line should not be included in coverage reports.

Added in version 8.0: Added pos field.

Changed in version 8.0: The name is changed to contain the mangled name previous content is now available as demangled_name as it is in GCOV JSON format.

Removed in version 8.0: Removed returned_count field because missing in gcov JSON format.

Added in version 7.0: New returned_count and branch_percent field.

Added in version 6.0: New gcovr/excluded field.

JSON Summary Output

The --json-summary option output coverage summary in a machine-readable format for additional post processing. The format corresponds to the normal JSON output --json option, but without line-level details and with added aggregated statistics. The --json-summary-pretty option generates an indented JSON summary output that is easier to read. Consider the following command:

gcovr --json-summary-pretty --json-summary example_json_summary.json

This generates an indented JSON summary:

{
    "root": ".",
    "gcovr/summary_format_version": "0.6",
    "files": [
        {
            "filename": "example.cpp",
            "line_total": 7,
            "line_covered": 6,
            "line_percent": 85.7,
            "function_total": 2,
            "function_covered": 2,
            "function_percent": 100.0,
            "branch_total": 2,
            "branch_covered": 1,
            "branch_percent": 50.0
        }
    ],
    "line_total": 7,
    "line_covered": 6,
    "line_percent": 85.7,
    "function_total": 2,
    "function_covered": 2,
    "function_percent": 100.0,
    "branch_total": 2,
    "branch_covered": 1,
    "branch_percent": 50.0
}

Added in version 5.0: Added --json-summary and --json-summary-pretty.

JSON Summary Format Reference

The summary format follows the general structure of the JSON Format Reference, but removes line-level information and adds aggregated statistics.

The top-level looks like:

{
  "gcovr/summary_format_version": version,
  "files: [file],
  "root": path,
  ...statistics
}

gcovr/summary_format_version: string

A version number string for the summary format. This is versioned independently from gcovr and the full JSON format. Consumers of gcovr JSON Summary reports should check that they are SemVer-compatible with the declared version.

Current version is:

“0.6”

files: list

Unordered list of file summary entries.

root: string

Path to the gcovr root directory, useful for reconstructing the absolute path of source files. This root path is relative to the output file, or to the current working directory if the report is printed to stdout.

…statistics

Project-level aggregated statistics. A NaN percentage (0/0) is reported as zero (0.0).

File summary entries

The file summary looks like:

{
  "filename": path,
  ...statistics
}

filename: string: Path to the source file, relative to the gcovr root directory.
…statistics: File-level aggregated statistics. A NaN percentage (0/0) is reported as null.

Summary statistics

The root and file summaries contain the following additional fields:

...
"branch_covered": ...,
"branch_total": ...,
"branch_percent": ...,

"line_covered": ...,
"line_total": ...,
"line_percent": ...,

"function_covered": ...,
"function_total": ...,
"function_percent": ...,
...

These fields can be described by the glob expression {branch,line,function}_{covered,total,percent}.

ELEMENT_covered: int: How many elements were covered or executed.
ELEMENT_total: int: How many elements there are in total.
ELEMENT_percent: float: Percentage of covered elements (covered/total) in the range 0 to 100. Note that the different contexts differ in their treatment of NaN values.