Find unused functions in C/C++ code with coverage analysis

Unused functions impact maintenance

Unused functions in a software project can cause code bloat, but they also create more work for the developers of tests, especially in the situation where code coverage (the quality) of tests is being measured. If a function is not used, then removing it from a project will reduce not only the complexity of the project, but also the amount of tests that need to be written for it. The problem of finding unused functions in software projects is that it can often be time consuming and frustrating.

Coco helps by displaying the function coverage of the execution of the program. In this tip of the week I would like to show you the perks of using Coco's Function Coverage for finding unused functions in your code project.

The example source code

For this presentation I'm using the following C code:

#include <stdio.h>
#include <string.h>

int A(char *arg)
{
    printf("A\n");
    return !strcmp(arg, "TRUE");
}

int B(char *arg)
{
    printf("B\n");
    return !strcmp(arg, "TRUE");
}

int C(char *arg)
{
    printf("C\n");
    return !strcmp(arg, "TRUE");
}

int D(char *arg)
{
    printf("D\n");
    return !strcmp(arg, "TRUE");
}

int main(int argc, char **argv)
{
    if ((A(argv[1]) || B(argv[2])) && (C(argv[3]) || D(argv[4]))) {
        printf("TRUE\n");
    } else {
        printf("FALSE\n");
    }
    return 0;
}

Instrumenting code, and running tests

We will first instrument the code with Coco's Coveragescanner tool. The result is an instrumented executable, and also a .csmes file which contains a database of code lines and their source locations.

$ csgcc -o prog example.c

Next, we run the instrumented program with specific arguments to cause it to execute a code path. This will create an execution report (.csexe file) which contains information about which code was executed. This file will be imported into the generated (.csmes file). As it turns out, with these arguments, the functions B and D are not hit by the test case.

$ ./prog TRUE FALSE TRUE FALSE

We can import the .csexe file into the .csmes file with the following command.

$ cmcsexeimport -m prog.csmes -e prog.csexe -t execution

The final step is to generate the report for the unused functions. Hereby we use the option --function-coverage to specify the coverage level. '--format-unexecuted=' prints the unused functions into the file result.txt by first writing the file( '%f') and then then line ('%l').

$ cmreport --function-coverage -m prog.csmes --format-unexecuted='%f %l' -t result.txt

Listing Unused Functions

The result.txt file contains now:

.../example.c 10

.../example.c 22

If we want to analyze more runs of the program, we can just run the ./prog command with different arguments. The executions will result in additional data concatenated to the .csexe file.

For further information about cmreport and other features of Coco, follow this link.