Library migration happens when a library can not meet the project's requirements and is non-trivial to accomplish. To mitigate the problem, substantial efforts have been devoted to understanding its characteristics and recommending alternative libraries, especially for programming language (PL) ecosystems with a central package hosting platform, such as Python (PyPI). However, to the best of our knowledge, understanding of C/C++ library migrations is still lacking, possibly due to challenges resulting from the fragmented and complicated dependency management practices in the C/C++ ecosystem. To bridge this knowledge gap, this paper analyzes 19,943 C/C++ projects that utilize different package management tools and establishes the first C/C++ library migration dataset. Based on the dataset, we investigate the prevalence, domains, target library, and rationale of C/C++ library migrations and compare the results with three widely investigated PLs: Python, JavaScript, and Java. We find that the overall trend in the number of C/C++ library migrations is similar to Java. Migrations across different package management tools are also observed. In C/C++, library migrations mainly occur in GUI, Build, and OS development, but are rare in domains (e.g., Testing and Logging) that dominate library migrations in the three compared PLs. 83.46\% of C/C++ source libraries only have one migration target, suggesting that our library migration dataset could be used directly to recommend migration targets. We find four C/C++-specific migration reasons, such as less compile time and unification of dependency management, revealing the unique dependency management requirements in C/C++ projects. We believe our findings can help C/C++ developers make more informed library migration decisions and shed light on the design of C/C++ library migration tools.